
The Diseases of the Sweet Pea 



THESIS 



PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL OF 
THE UNIVERSITY OF PENNSYLVANIA IN PARTIAL FUL- 
FILMENT OF THE REQUIREMENTS FOR THE 
DEGREE OF DOCTOR OF PHILOSOPHY 



J. j. TAUBENHAUS 



PHILADELPHIA 
1914 



The Diseases of the Sweet Pea 



THESIS 



PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL OF 
THE UNIVERSITY OF PENNSYLVANIA IN PARTIAL FUL- 
FILMENT OF THE REQUIREMENTS FOR THE 
DEGREE OF DOCTOR OF PHILOSOPHY 



J. J. TAUBENHAUS 



PHILADELPHIA 
1914 



SB €08 






BULLETIN NO. 106 NOVEMBER, 1914 

Delaware College 

Agricultural 

Experiment Station 







The Diseases of the Sweet Pea 



BY J. J. TAUBENHAUS 



* •-. 



Newark, Delaware 



INDEX 

The Host 3—10 

Taxonomy and Botany 3 — 

History of the Sweet Pea • • 5 — 6 

Economic Importance 5 6 

Cultivation and Care ■ • 6 — 8 

Sweet Peas Under Glass 8 — 10 

Diseases of the Sweet Pea 10 — 74 

I. Fungous Diseases 12 — 68 

II. Bacterial Diseases 68 — 72 

III. Physiological Diseases 72 — 74 

A. Root Diseases ■ ■ 12 — 36 

B. Diseases of the Aerial Parts of the Plants 36—65 

C. Diseased Seeds 65—68 

Root rot (Thielavia basicola Zopf) 12 — 21 

Rhizoctonia root rot (Corticium vagum B. & C.) 21 — 27 

Chaetomium root rot (Chaetomium spirochaete Patt.) . . 27 — 30 

Fusarium root rot (Fusarium lathyri Taub.) 31 — 34 

Root Knot (Heterodera radicicola [Greef] Muller) 35—36 

Stem or collar rot (S. libertiana Fckl.) 36 — 41 

Powdery mildew (Oiduim sp.) 41 — 43 

Anthracnose (Glomerella rufomaculans) 43 — 55 

Mosaic disease 56 — 64 

Diseases not known to be present in this country 64 — 65 

Pea blight (Peronospora trifoliorum De By.) 64 — 65 

Pea spot (Ascochyta pisi Lib.) 65 

Diseased seeds 65 — 68 

Streak disease (Bacillus lathyri M. & T.) 68—72 

Bud drop • • 72 — 73 

Arrested development 73 — 74 

Methods of Control 74—76 

Resistant varieties 76 — 80 

Seed treatment • • 76- — 80 

Treatment of Soil with Chemicals 80 — 82 

Studies of the Fungicidial value of some chemical poisons 82 — 85 

Soil treatment in the greenhouse 85 — 87 

Summary 85 — 89 

References •■ ■ 88 — 93 



THE DISEASES OF THE SWEET PEA 

BY J. J. TAUBENHAUS 



THE HOST 

TAXONOMY AND BOTANY 

The sweet pea (Lathyrus odoratus L.) belongs to the family 
Leguminosae, the sub family Papilionaceae, the tribe Vicieae. The 
sweet pea (Lathyrus odoratus L.) is a herbaceous vine with rough 
stems, hairy and winged. The leaves are alternate, pinnately com- 
pound with terminal tendriliform leaflets. The leaflets are oval or 
oblong, mucronate. Peduncles 2-4 flowered, much longer than the 
leaves. The calyx teeth are broad, longer than the tube. The flowers 
are large, and showy in shades of blue, red, yellow and White. The 
standard is large, expanded, hooded, or wavy. The legumes are com- 
pressed, linear, 1-3 inches, hairy. The seeds are round, sometimes 
angled, black, white or mottled. 

HISTORY OF THE SWEET PEA 

Origin, Improvement and Distribution**. The word "Lathy- 
rus" is from the Greek La. la (augmentative) and thouros, anything 
exciting, having reference to the qualities of seeds of certain species. 
In Europe the species of Lathyrus are known as "Gesse, " the sweet 
pea being known as Gesse odorante. The French know the plant under 
this name, or as Pois Odorante, or Pois de Senteur. " 

The earliest mention of the sweet pea is found in ' ' Sillabus Plant- 
arum Sicillge-nuper detectarum a P. F. Franciscus Cupani" 
(Panormi, 1695). The sweet pea is spoken of as "Lathyrus distoplat- 
yphyllos hirsutis mollis, magno et peramoeno flore odore." Father 



*Also presented to the Faculty of the Graduate School of the University of 
Pennsylvania, June 1913, as a major thesis in partial fulfillment of the require- 
ments for the degree of Doctor of Philosophy. 

Acknowledgements. — The writer is indebted to Dr. John W. Harshberger, 
under whose direction the work was conducted, for helpful suggestions and crit- 
icisms. Acknowledgements are also due to Dr. T. P. Manns for helpful sugges- 
tions and advice. Thanks are also due to the many American seedsmen for finan- 
cial support in carrying out the field experiments. 

**A11 references will be found on pp. 8^o 93. 



Cupani was very enthusiastic about this flower and in 1699 sent seed 
to Dr. Uvedale at Enfield, England, and to Caspar Commelin at Am- 
sterdam, Holland. Commelin described and illustrated the plant in 
his "Hort.-Medici Amstelodamensis " (1697-1701). Commelin also 
adopted Cupani 's name for the plant. 

In his "Almagesti Botanici Mantissa" (1700) Dr. Leonard 
Plukenet also gives a description of the sweet pea. A dried specimen 
preserved in Plukenet 's Herbarium, which now forms part of Sir 
Hans Sloane collection, is the oldest specimen of the sweet pea in ex- 
istence. 

Mention is made of the sweet pea by Petiver in the "Botanicum 
Hortense III" (1713). Petiver calls the plant Lathyrus Siculus, a 
native of Sicily which has large broad sweet smelling flowers. H. B. 
Ruppii in "Flora Jenensis" (Frankfort, 1718) places Lathyrus 
Siculus Ravini in a class of plants with irregular flowers. It is thus 
seen that all authorities place Sicily as the home of the sweet pea. 

Linnaeus, 1753, in his great "Systema Plantarum Europse," 
classifies the sweet pea as follows: 

"Odoratus II. Lathyrus pedunculis bifloris, cirrhis 

diphyllis, foliis ovato-oblongis, leguminibus hirsutis. Hort. 

Cliff. 368, Hort. Upsal. 216, Roy. lugd. 363. 

"Siculus a. Lathyrus Siculus. Rupp. jen., 210 

Lathyrus distoplatyphyllos hirsuitis mollis, magno et per- 

amceno flore odoro. Comm. Hort. 2, p. 219, t. 80. 

"Zeylanicus b. Lathyrus Zeylanicus. Odorato flore amcene 

ex albo et rubro vario. Burm. Zeyl., 138. 
' ' Habitat : a. in Sicilia ; b. in Zeylona. ' ' 

Here then is the first use of the term ' ' odoratus " as a distinctive 
name. 

Kniphof in his "Botanico in originali" (1757-1763) gives a col- 
ored illustration of Painted Lady sweet pea. In the catalog of ~W. 
Malcolm (1778), seedsman of Kensington Turnpike, we find offered 
for sale, white, purple and Painted Lady sweet peas. The first evi- 
dence of improvement is noticed in the catalog of John Mason (1793). 
He offered black, purple, scarlet, white and Painted Lady sweet peas. 
Between 1845 and 1849 the firm of Messrs. J. Carter & Co. introduced 
a new striped sweet pea and a new large purple sweet pea. In 1850 
Messrs. Nobel, Cooper and Bolton introduced a new large dark pur- 
ple variety. In 1860 Mr. Carter offered several new varieties of sweet 



peas. In James Vick's "Illustrated Catalog and Flower Guide" 
(1870), nine varieties of sweet peas are mentioned. 

Beginning with 1880, great strides have been made in the im- 
provement of "the sweet pea in England. Thomas Laxton and Henry 
Eckford (about 1880) were the moving spirits. Mr. Laxton intro- 
duced several new varieties obtained by crossing. Mr. Eckford was 
responsible for one hundred and fifteen new varieties. In America, 
Edward Sayers in his book "The American Flower Garden Com- 
panion" Boston, 1838), gives a list of five varieties of swee't peas. Of 
the American pioneers and breeders of the sweet pea, those who should 
be mentioned are D. M. Ferry & Co. who in 1889 introducd the 
Blanche Ferry; W. Atlee Burpee & Co., Messrs. C. C. Morse & Co., 
J. C. Vaughn and Peter Henderson. 

During the first one hundred years of sweet pea culture only three 
varieties, or colors, were known, i. e., purple with blue wings, pale red 
with white wings (Painted Lady) and white. The black and the scar- 
let appeared in the last years of the eighteenth century. At the pre- 
sent time there are more than a hundred and fifty varieties in cultiva- 
tion with promising new ones appearing every year. This shows the 
great popularity of the sweet pea and the extent to which it is grown. 
Whenever a crop is grown extensively and for a long time under cer- 
tain soil and climatic conditions, as is 'the sweet pea, diseases are sure 
to appear, making it difficult for the crop to succeed unless precau- 
tionary measures are taken. The cultivation of the sweet pea in Eng- 
land is at a crisis, the disease factor being the one obstacle to its cul- 
tivation. In America sweet pea growers are confronted with several 
important diseases. 

ECONOMIC IMPORTANCE 

I have been unable to obtain statistical data concerning the sweet 
pea crop. Messrs. C. C. Morse & Co. furnished us with the following 
information : 

"Your favor of the 8th inst. was duly received and I shall be very 
glad to answer the questions you have asked, as well as I can. 

"However, our Sweet Peas will be practically a failure this year 
and my statistics will apply only to past seasons, probably more ac- 
curately to the crop of 1911, which was the best we have had in recent 
times. Even last year's crop was very poor. 



1. So far as seed is concerned, the Sweet Pea crop is 
worth about $250,000 annually to the grower. 

2. There are about 1700 acres of land planted to Sweet 
Peas for seed in California annually. I have no knowledge 
of what acreage is devoted to flowers for market. 

3. Practically no Sweet Pea seed is imported and about 
one-half of the California acreage is exported. 

4. Fully 90 per cent, of the export business is done with 
Great Britain; the balance with Holland, Germany and 
France. 

5. No other country, so far as we know, produces Sweet 
Pea seed to amount to anything. 

Respectfully yours, 

C. C. MORSE & CO." 

According to Bailey 2 , California, in 1902, supplied the world's 
market with 125 tons of sweet pea seeds. As a cut flower the sweet 
pea is a great favorite and is extensively grown for that purpose. 

CULTIVATION AND CARE 

In this connection we will consider only those points of culture 
which directly influence the disease factor. 

Climate. The sweet pea does best in a temperate region. It 
will not stand too warm a climate, as the plants there soon dry up 
and die, or they are so weakened as to succumb readily to all sorts of 
fungous diseases. California seems to be its ideal home, nevertheless 
the sweet pea is known to thrive under various climatic conditions. It 
is less susceptible to cold than to heat and in hot dry climates irri- 
gation is essential. 

Site. The sweet pea requires an open, sunny location so as 
to get plenty of light and air. Plants grown in too shady a place 
will be spindly, weak, and open to the attacks of diseases. 

Soil. All light sandy soils should be avoided for the reason 

already referred to above. A good loamy soil is preferred provided, 
of course, its subsoil is well underdrained, otherwise the plants will 
grow poorly and be constantly open to the attacks of disease. 

Fertilizer. In order to be at their best, sweet peas must be 
provided with sufficient available plant food in the soil. However, 



fertilizers should be used very judiciously. The aim should be to apply 
a food that is well balanced, i. e., it should contain the proper amount 
of nitrogen, phosphorus, potash and lime. Too much of one of these 
elements and too little of the other will produce disturbances in the 
metabolism of the plant as will be seen later under the discussion of 
physiological diseases. For an ordinary garden land, the following 
is a well balanced fertilizer devised by Prof. T. F. Manns of the Del. 
Expt. Station. Before plowing a surface application of well rotted 
manure at the rate of 6 tons per acre is first applied to the soil. After 
plowing and harrowing the soil, it is furrowed and 5 tons of rotted 
manure per acre is applied in the furrows. The manure is worked in 
deep with a spade and the following fertilizer is applied in the 
furrows : 



*Sodium nitrate 


200 lbs. per acre 


Dried blood 


250 lbs. " " 


Acid phosphate 


1200 lbs. " 


Potassium sulphate 


240 lbs. " " 


Rock phosphate 


400 lbs. " " 


Hydrated lime 


200 lbs. " " 


Carbonate of lime 


600 lbs. " " 



The fertilizer is well mixed up with the soil and the seeds are 
planted on top and covered to a depth of about two to three inches. 

Care of the Seeds and Depth of Sowing. Most of the white- 
seeded varieties are subject to decay in the soil. Most of the black- 
seeded varieties are more resistant to soil decay but they do not ger- 
minate evenly. In order, therefore, to hasten germination, it is ad- 
visable to place the seed in tepid water over night. With this treat- 
ment the seeds swell and are ready to be sown the next day. The Rev. 
W. T. Hutchins, a well-known sweet peas specialist in America, advises 
the placing of the seed in moist earth for seven or eight days. They 
are then taken out and examined. The swollen seeds are planted and 
the hard seeds cut with a knife to hasten germination. Whatever 
method is used the aim should be to hasten germination in order to 
prevent the seed from laying too long in the ground and thereby caus- 
ing decay. The depth of sowing the seeds varies from two to three 
inches according to the nature of the soil. As to distance, five feet 



*This mixture was recommended for a very heavy acid soil deficient in or- 
ganic matter. 



apart between the rows and three inches in the row will insure the de- 
sired amount of air and light. 

Care of the Growing Plants. Frequent cultivations with the 
hoe or with the cultivator will provide sufficient aeration of the roots 
to insure a vigorous growth of the vine. It is in baked and ill-drained 
soils that saprophytic fungi assume the nature of semi parasites, since 
it is in these soils that the plants are often weak and consequently 
yield readily to the attacks of disease. Moreover, frequent cultivations 
destroy the weeds which may act as disease carriers or disease trans- 




A convenient way of trailing sweet peas 



mitters. Irrigation wherever possible will no doubt benefit the plants, 
but irrigation should not replace cultivation. The plants should 
be kept free from the insect and the fungus pests. This will be dis- 
cussed under methods of control. With the sweet pea, contrary to 
many other flowering plants, the blooms should be gathered freely as 
the more we do this the longer the vines will continue to flower. 



SWEET PEAS UNDER GLASS 

The following notes on cultivation are by Mr. William Sim, Clif- 
tondale, Mass., and are extracted from a paper read by him before 
the Gardeners' and Florists' Club of Boston on April 21, 1908: 

' ' To grow the sweet pea to perfection under glass you must have 
a greenhouse suitable for the purpose. It should be at least eight feet 
high on the sides, four and a half feet being glass. My houses are 
seven feet, and I find the side rows strike the glass when the vines are 
about half grown, thereby giving me half a crop. My center rows are 
about right ; they are twelve to fifteen feet high. The higher the vines 
grow the more and better flowers you get. We plant the rows five 
feet apart and in a line with the supports of the greenhouse. The up- 
rights are twelve feet apart, so in supporting we run twine from one 
support to the other on each side of the row. This I have found the 
best method of supporting. I have tried wire netting; it is only a 
nuisance, as the vines do not cling to the wire, which causes just as 
much tying as if it were not there. It also causes injury many times 
to the vines, as a sweet pea stretches many times more than a foot in 
developing; if held back by anything in growing the growth looks 
like a spiral spring, and the picking of the blooms is made very dif- 
ficult. The side rows are planted five feet from the sides of the house ; 
and all the heating pipes are on the sides. The vines are very suscep- 
tible to red spider and as they will not stand syringing, the further 
you can afford economically 'to have them from the pipes the better. 

' ' We have not changed the soil in the houses since they were built 
four and five years ago, and we find the vines are getting more vig- 
orous each year. In the same soil a crop of tomatoes and of violets 
is harvested each year. The soil was originally eighteen inches deep, 
but by the application of manure each year the depth is now 'two and 
a half feet. The tomato crop is on the wane the middle of August. 
When these are cleaned out we trench the house over as deep as the 
soil, bringing the bottom soil to the surface. In the bottom of the 
trench we put three inches of decomposed cow manure ; one foot from 
the surface we put on three inches more of the same material. The 
house is allowed to remain in this state until nearly time for sowing 
the seed. The soil is then usually very dry, so we dampen it down 
enough to cling together while the house gets another forking over. 
This time we go down one foot and mix the top layer of manure with 
the surface soil. We then make the surface as nearly level as pos- 



8 

sible and thoroughly water the soil, giving enough to penetrate the 
entire mass, with a strong dose of liquid horse manure. In about 
three days, depending on the weather, the house will be ready to plant. 
We sow 'the seeds about one and a half inches apart. We make the 
drills one inch deep and do not allow more than one inch of soil over 
them. We do not pull any more soil toward the roots, as is often 
recommended, but let it remain level. If more soil is pulled around 
the base of the plant, stem rot is sure to follow. We do not water the 
plants again until they are up about three inches. 

"Of course, you can grow them on a bench with a few inches of 
soil, but the results will be just what you make them — a weak growth 
and a crop of short-stemmed flowers. These soon play out, as there is 
not enough soil or food for the vines to live on. 

"They may be made to flower any time you wish by increasing 
the temperature, but the best results are obtained by growing at a 
temperature just above freezing until the buds can be felt in the 
crowns of the plants. Then the temperature should be gradually in- 
creased, say one degree a night, until you reach 48 degrees. This, I 
think, is about right, although in midwinter I think they move a little 
better at 50. As the days lengthen a little cooler temperature seems 
to suit better. A rise of 10 to 15 degrees should be given during the 
day in sunny weather. In spells of cloudy weather 55 degrees is high 
enough during the day. If a high temperature is given in dark 
weather the growth gets soft and wilts when the sun comes out bright 
again. While the plants are young they should be regularly fumigat- 
ed so there will not be a sign of lice when the plants commence to 
flower. If they are clean at this stage it will not be necessary to fumi- 
gate while they are in bloom. It is impossible to sell sweet peas that 
smell of tobacco. Tobacco also bleaches the flowers of some varieties, 
and makes them look like some other variety. 

"We sometimes hear of someone having trouble with the buds 
dropping. This is more the case in midwinter than at any other time, 
and is caused by a too cool temperature or a sudden chill, or too much 
water. Should a house be allowed to go near the freezing point in 
midwniter the wholesale dropping of buds will be sure to follow." 



9 

DISEASES OF THE SWEET PEA 

HISTORICAL 

The literature on the subject of sweet pea disease previous to 1906 
is mostly of a fragmentary nature. In 1896 Cuthbertson 3 first records 
a bud and blossom drop of the Cupid sweet pea in Scotland attributing 
■the cause to cold and damp weather at that time. 

In 1906, Massee 4 gave the first brief scientific account of some 
sweet pea diseases, mentioning the following fungi: Peronospora tri- 
foliorum, P. viciae, Erysiphe polygoni, and Ascochyta pisi. 

In 1906, Weston 6 was first to describe the "Streak" as a new dis- 
ease of the sweet pea in England (the cause not given) . In 1907, "Wes- 
ton 6 again calls attention to the serious nature of the "Streak." 

In 1907, an anonymous note 6 mentions the following diseases: 
eelworm (Tylenchus devastatrix and obtusa), Peronospora trif olio- 
rum,, sclerotia of some species of Sclerotinia, Erysiphe martii, and 
Botrytis cinerea. 

In 1909, in a brief note, Massee 7 also mentions the "Streak" dis- 
ease which he thinks is induced by an excess of manure in the soil. 
This excess produces a deleterious effect on the soil flora which in turn 
brings about physiological disturbances resulting in the "streak." In 
1912, Massee 8 again mentions a disease of sweet pea seedlings and of 
other plants as due to Thielavia. 

In the same year (1912) Chittenden 9 , before the London Sweet 
Pea Society and in an article in the Royal Horticultural Society Jour- 
nal reports on the "Streak" disease, which according to him, was 
found to be due to Thielavia basicola. 

In 1912, W. Dyke 10 , an amateur scientist and gardener, calls 
attention to the "streak" disease which he believes is induced by a 
species of Fusarium and Macrosporium. It will be seen from the 
above reference that the only ones of scientific importance are those 
of Massee and Chittenden, because both of these investigators base 
their facts on research. However, as it will be shown later, both 
Massee and Chittenden mistook Thielavia as the cause of the "Streak" 
disease. 

In American literature, Sheldon^ was the first one to call atten- 
tion to the anthracnose of the sweet pea (Grlomerella ruf omaculans. ) 

The diseases of the sweet pea have received no other attention at 
the hands of American plant pathologists. 



10 ■ 

For the past three years the writer has been investigating the dis- 
eases of the sweet pea, and as a result three papers have already been 
published 12 . 

It is the purpose of the present thesis to bring together all the re- 
sults obtained in my investigations. The subject is by no means ex- 
hausted, as yet, and we hope to devote many more years to the study 
of the diseases of the sweet pea. 

THE DISEASES OF THE SWEET PEA 

The diseases treated in this thesis are as follows : 
I. Fungous Diseases. 

II. Bacterial Diseases. 

III. Physiological Diseases. 

IV. Animal or Insect Pest (Of the animal pests I will only con- 
sider the Heterodera radicicola and will discuss it under "root dis- 
eases. ' ' Of the insect pests I will only consider the green aphids and 
these will be discussed in relation to the "mosaic." 

I. Fungous Diseases 

A. Root Diseases. 

B. Diseases of the Aerial Parts of the Plants. 

C. Diseased Seeds. 

A. Root Diseases 

All root troubles of the sweet pea are caused by fungi which live 
primarily in the soil. They can, therefore, also be designated as soil 
diseases. Diseased roots invariably indicate an infected soil. All 
soil parasites are not necessarily confined to the roots of the sweet 
pea only, as we shall have occasion to show later. Of the soil organ- 
isms which attack the roots, the following have been investigated : 

Root rot. (Thielavia basicola Zopf.) 

Root rot. Rhizoctonia (Corticium Vagum B. & C.) 

Root rot. ( Chaetomium spirochaete Patt. ) 

Root rot. (Fusarium lathyri n. sp.) 

Root galls Eel worms (Heterodera radicicola.) 

ROOT ROT {Thielavia basicola Zopf) 

Historical, Synonymy and Relationship. Thielavia basicola 
belongs to the ascomycetous family Perisporiacese. The fungus was 



11 

first described by Berkeley and Broome 13 in 1850, who gave it the name 
of Torula basicola; they found it growing at the base of affected pea 
plants. The torula or chlamydospore stage is the most conspicuous 
and it is abundantly found on the host. In 1875, Zopf 14 found the 
fungus on roots of Senecio elegans in Berlin, and in 1876, Sorokin 15 
found it on the roots of Cochlearia armoracia (horse radish) in 
Eussia, and named it Helminthosporium fragile. Zopf, however, made 
a more thorough study of the fungus, and he discovered the perfect 
stage, placing it in the PerisporiaceaB, creating a new genus Thielavia 
after Prof. F. von Thielav of the University of Berlin. 

In 1886 Saccardo 16 found the same fungus. Noting the observa- 
tions of Sorokin, he did not agree with him in calling the fungus Hel- 
minthosporium, and he placed it in the genus Clasterosporium. Sac- 
cardo thus failed to identify Sorokin 's Helminthosporium fragile with 
the chlamydospore stage of Thielavia and with Berkeley and 
Broome's Torula basicola. It was to the credit of Sorauer 17 who dis- 
covered the relationship of these different stages to belong to one and 
the same fungus. The name of the fungus with its synonomy is as 
follows : 

Thielavia basicola (B. & R.) Zopf. 
Torula basicola (B. & R.) 
Helminthosporium fragile Sor. 
Clasterosporium fragile (Sorok.) Sacc. 

Thielavia a Parasite on Other Hosts. The table on page 12 will 
show the list of hosts parasitized by Thielavia together with the au- 
thority for the same. 

Thielavia Attaching Sweet Peas. In 1912, Chittenden 18 was 
asked by the National Sweet Pea Society of England to investigate the 
dreaded "Streak" disease of the sweet pea. In his report before that 
society Chittenden gives an accurate description of the "Streak," 
so that there can be no doubt but that he had the disease well in mind, 
that is, he described it as a stem disease. Chittenden found Thielavia 
basicola to be the cause of "Streak" as he states, "careful micro- 
scopic examinations of the brown patches of the roots, and one must 
insist on the need for care ; hasty examination may fail to reveal any- 
thing showing that they were attacked by a fungus whcih turned out 
to be Thielavia basicola. The same fungus was present in practically 



12 

Name of Plant Authority 

Aralia quinquef olia Selby 

Begonia rubra Selby 

" sp Zopf 

Catalpa speciosa Selby 

Cochlearia armoracia Sorokin 

Cyclamen Sorokin 

Gossypium herbaceum Smith, E. F. 

Lupinus albus Zopf 

Linaria canadensis Gilbert 

Nemaphila auriculata Berkeley and Broome 

Nicotiana tabacum Selby, Gilbert, Clinton 

Onobrychis crista — galli Zopf 

Oxalis corniculata Gilbert, Stewart 

Pisnm sativum Berkeley and others 

Phaseolus vulgaris Zopf 

Trigonella coerulea 

Vigna sinensis Smith, E. P. 

Viola odorata Thaxter and others 

Trif olium repens Gilbert and Stewart 

Lathyrus odoratus Taubenhaus 

every case, sometimes abundantly fruiting, sometimes with only a few 
spores." 

I will show later where Chittenden has erred in his investigations, 
and that the "streak" is not a root but a stem disease which is in- 
duced by a bacterium and not by Thielavia. In every case where 
Thielavia has been reported as a parasite on other hosts, it has been 
found on the roots and not on the stem. This same holds true for 'the 
sweet pea. Moreover, Chittenden in his artificial inoculation with the 
fungus, has succeeded in reproducing the typical root rot and not the 
"streak" on the stems. Massee 19 too made the same mistake as Chit- 
tenden, for he too considers Thielavia to be the cause of the "Streak." 
I have seen 'the Thielavia root rot on half an acre of sweet peas at the 
trial grounds of one of our commercial seed men. The plants on that 
infested area were carefully examined, and no signs of streak could be 
found on, the stems. On the other hand, the trouble was seen to be 
plainly localized at the roots. 

Symptoms of Thielavia Boot Rot on Sweet Peas. Plants severely 
infected have practically little or no root system since the latter is 
destroyed by the fungus as rapidly as the roots appear. (Figs. 
1 and 2). Whatever root system is present is of a stubby nature and 




Fig 1* Boot rot caused by Thielavia. Contrasting a healthy with a diseased 

plant of the same age. 
* Figs. 1, 2, 9, 17, 33, 34, 35, 37, 39, 40 and 42, Electrotype, Gardener s Chron- 
icle (England). Photographs by the author. 



14 



charred in appearance. The fungus sometimes works upon the stem 
to a distance of two to three inches above ground, but never to the 
extent of invading the entire stem. It is probably due to this that 
some workers have mistaken 'this disease for the well-known "streak." 




Fig. 2. Eoot rot caused by Thielavia. Comparing root systems of healthy plants 
with diseased plants of the same age. 



15 

Sweet peas infested with Thielavia have a dwarfed and sickly appear- 
ance. The fungus does not seem to kill it, but merely to produce an 
arrested development. The infected plants are useless for commer- 
cial purposes, as they fail to set flowers. 

Pathogenicity. Chittenden 20 seems to have been unable to in- 
fect healthy sweet pea seedlings with the fungus Thielavia basicola 
under normal conditions of growth. It was only when his plants were 
overwatered that the fungus became an active parasite. 

In my own inoculation experiments, healthy sweet pea seedlings 
have been readily infected by placing a pure culture of the fungus on 
the roots of the plants growing in sterile soil. In two to three weeks 
the roots were thoroughly diseased. Overwatering was not found nec- 
essary to bring about infection, although such treatment as well as 
injury to the roots favor the fungus in its activity. Another method 
adapted for proving the pathogenicity of the fungus was to sow pure 
cultures of the fungus together with sterilized seed (seeds treated in 
a solution of formaldehyde, 5 parts in 100 of water for 1-2 hr.) 
in sterile pots and soil. Checks were also sown with sterilized seeds 
in sterile pots and soil but without the fungus. Six days after sow- 
ing both lots of seeds germinated and both check and infected seed- 
lings apparently grew equally as well. Beginning with the third 
week, infected seedlings ceased growing, whereas the checks made con- 
siderable progress. After six weeks the infected seedlings were seen 
to be decidedly dwarfed and pale green in color reproducing the typ- 
ical symptoms of the disease as observed in the field. The check seed- 
lings have by this time made decided growth. An examination of the 
roots of the infected seedlings revealed a diseased condition as found 
in the field, namely, absence of a well developed root system, and a 
blackening of the affected parts. The infection experiments were re- 
peated five times always with the same result. In no case was the Thie- 
lavia seen to kill the host, but in each case a dwarfed condition of the 
plant was the result. 

Infection of Sweet Peas with Thielavia from Other Hosts. It 
was found desirable to determine whether there existed any racial 
strains or physiological species of Thielavia basicola. Accordingly, 
pure cultures of the fungus obtained from cowpea, violets, parsnip and 
tobacco, were inoculated on sweet peas, using the same method of in- 
oculation as previously described. In connection with this experiment 



16 



a parallel series of inoculations was also run, using 'the Thielavia basi- 
cola from the sweet pea. The results obtained were the same, i. e. the 
Thielavia fungus when taken from other hosts than the sweet pea will 
readily infect the sweet pea, thus showing the absence of physiological 
strains or species. 

Morphology of Thielavia basicola. Our studies and observa- 
tions on this fungus have brought out facts found by other investiga- 
tors. The mycelium of the fungus is hyalin, septate and branched. 
The hyphas average from 3-4 u in width. The mycelium becomes more 
or less greyish with age. There are three kinds of spore forms pro- 
duced. 1. Endospores, so called because they are formed inside a 
special thread of the mycelium. This is the spore form that is most 
commonly met with in pure cultures of artificial media. The endo- 




Fig. 3. Endospores. 

Figs. 4, 5. Chlamydospores breaking up into individual spores. 

Fig. 6. Chlamydospores, unbroken. 

Fig. 7. Ascospores. 

Fig. 8. Ascus. 

spore case is formed on terminal branches. It has a somewhat swol- 
len base and a long tapering cell (Fig. 3). The endospores are form- 
ed in the apex of this terminal cell and are pushed out of the rup- 
tured end by the growth of the unfragmented protoplasm of the base. 
They are hyalin, thin-walled, oblong to linear 10-25 u x4-5 u . 

The second kind of spores formed are the chlamydospores (Figs. 
4-6). These are thick-walled dark brown bodies, born on the same 
mycelium as the endospores, and average from 20-50 u xl0-18 u , and 
correspond to the Torula stage of Berkeley's classification. 



17 

The third kind of spores are the aseospores (Fig. 7.) These are 
lenticular in shape 12x5" and are born in asci which in turn are born 
in spherical black perithecia. "We have not as yet found the asco- 
spore stage (Fig. 8) on the affected host, altho it is said to appear 
quite commonly on other hosts affected by this fungus. 

Peglion 21 in 1897 was apparently the first to grow the fungus 
in pure culture. Aderhold 22 in 1903 reports to have grown the fun- 
gus in pure culture. Clinton 23 and Gilbert^ experienced considerable 
difficulty in obtaining a pure culture of the fungus, due to the fact 
that the chlamydospores when taken from old diseased roots fail to 
germinate by being overrun with bacteria. At no time did the writer 
experience any difficulty in obtaining a pure culture of Thielavia from 
diseased sweet pea tissue. The following method was adapted from 
Manns 25 . Portions of the diseased roots are placed in a test tube in a 
solution of 1-1000 HgCl 2 in a 50 per cent, alcohol and thoroughly 
shaken for thirty seconds. This will kill all surface contaminations. 
The disinfectant is then poured out and the material is rinsed three 
times in sterile water, the object being to remove all traces of mer- 
curic chloride. Each tissue fragment is then taken separately and 
crushed with a sterile forceps in a tube of medium which has been melt- 
ed and cooled to the proper temperature. The crushed tissue is now 
mixed with the medium in the tube, and the whole poured into a petri 
dish. After five or six days a pure growth of the fungus appears in 
the petri dish. The growth in this case resulted from the mycelium 
which has been crushed and liberated from the deeper tissue. 

The fungus will grow on a variety of media. It grows well on 
sterilized vegetable plugs as those of potato, beet, carrot, sweet potato, 
corn stalks, and parsnip and particularly well on corn meal. Both 
endospores and chamydospores are produced on these media, but in no 
case did I obtain the perfect stage, although it was often looked for. 
Previous investigators too have never succeeded in obtaining the asco- 
spore stage on pure culture. 

Pathological Conditions of the Diseased Host. Reference has 
been previously made to the fact that the disease produced by Thie- 
lavia is confined to the root system. Infected plants have little or no 
root system at all, or if present it is charred and invaded by the fun- 
gus. The question arises, how do the plants persist such a long time 
without collapsing? It was observed that sweet peas affected with 



18 

Thielavia, constantly make an attempt to produce new roots, but as 
fast as they are formed they are invaded by the fungus. It is possi- 
ble, therefore, that these new rootlets help the host to persist so long, 
and yet not long enough to enable it to make any growth. It is also 
probable that there is a close symbiosis between host and parasite with 
the latter getting the upper hand. As far as observed from cross sec- 
tions of that part of the stem which lies closest to the roots, the fun- 
gus is seen to invade all parts of the tissue with the exception of the 
xylem vessels. This fact, that the fungus does not enter the conduct- 
ing vessels permits an upward movement of the water, and this is suf- 
ficient to prevent the host from dying. 

ROOT ROT, Corticium vagum B. & C. 

Historical data, European literature. The first mention of 
Rhizoctonia can be traced to Duhamel 26 who in 1728 described a dis- 
ease of Saffron (Crocus sativus). He considered the sclerotia to be a 
special plant and the hyphae its roots, and named it Tuberoides. In 
1782 Fougeroux de Bondaroy 27 found asparagus plants which grew 
near a diseased saffron field to be likewise affected with Tuberoides. 
The first attempt to place the fungus in a systematic position was made 
by P. Builliard 28 who referred it to the Truffles- as Tuber parasiticum. 
Persoon 29 placed it in the Genus Sclerotium, and called it Sclerotium 
crocorum. De Candolle 30 was first to use the name Rhizoctonia. He 
at that time distinguished three species, R. crocorum, R. medicaginis, 
and R. mali. Nees 31 in 1817 refers to a fungus disease of the crocus 
which he calls Thanatophytum crocorum. From an examination of 
his figures there can be no doubt but that it is Rhizoctonia. In 1830, 
Duby 32 described a fungus disease of Allium ascalonicum and named 
it Rhizoctonia allii. In 1843 Leveillee 33 describes Rhizoctonia as at- 
tacking Rubia tinctorum, Solanum tuberosum, Phaseolus, and other 
plants. (The species of Rhizoctonia is not stated.) In 1851 the 
Tulsane 34 Brothers placed all the known forms of Rhizoctonia in one 
species which they called Rhizoctonia violacea. However, from Kuhn's 
critical work a few years later, it seems advisable to maintain the dis- 
tinction between R. solani and R. medicaginis. In Kukn's 35 work 
which was published in 1858, a brief account is given of the smooth 
sclerotia of R. solani contrasted with the wooly sclerotia of R. 
medicaginis. Distinction is also made of R. crocorum and R. medi- 
caginis, the latter is stated to attack beets and carrots. In 1903 



19 

Erikson 36 concerns himself chiefly toward 'the discovery of biologic 
forms of the fungus. 

In 1905, Gussow 37 described the disease on potato and lucern, and 
he considers R. solani and R. violacea as one and the same. 

In 1912 Shaw 38 investigated the morphology and parasitism of 
Rhizoctonia with a view of obtaining a better understanding of the 
supposed different species. Shaw concludes that the name R. violacea 
should be retained for all the non-fruiting forms with macrosclero- 
tia, and the name Corticium vagum be given to the fruiting stage of 
the macrosclerotia of R. violacea, while the forms with microsclerotia 
should be identified as R. solani Kuhn. 

American Literature on Rhizoctonia. The American references 
to Rhizoctonia are as follows: 

In 1891 Pammel 39 describes a rot of the beet root which he at- 
tributes to Rhizoctonia betae Kuhn. 

In 1892 Atkinson 40 found a sterile fungus causing a damping-off 
of cotton, which he called "sore shin." The fungus can no doubt be 
referred to as Rhizoctonia. Later, Stone and Smith 41 give an account 
of a lettuce disease due to Rhizoctonia. 

In 1901 Duggar and Stewart 42 describe extensively a list of hosts 
attacked by Rhizoctonia. However, the species of the fungus is not 
given. 

In 1904 Rolfs 43 reports on a potato disease due to Rhizoctonia, in 
which he found the fertile stage Corticium vagum B. and C. Speci- 
mens were sent by Rolfs to Dr. E. A. Burt, who pronounced it a va- 
riety of Corticium vagum B. and C. and for which he has suggested 
the name Corticium vagum B. and C. var. solani Burt. 

In 1909 Stevens and Hall 44 described a disease of the apple, pear 
and quince, which they attributed to a sterile fungus Hypochnus och- 
roleuca Noack. The fungus is described as having small sclerotia and 
there is no doubt but that it is a Rhizoctonia. Several workers have 
claimed to have connected different fruiting stages with that of 
Rhizoctonia. In 1869 Fuckel 45 stated that the Ascomycete Byssothe- 
cium circinans Fckl. was the perfect form of Rhizoctonia, both stages 
were found on decaying stems of Medicago sativa. Prunet 46 also ob- 
served this association of Rhizoctonia on lucern with an ascomycete. 

Hartig 47 found a Rosellinia associated with a Rhizoctonia on the 
roots of oak. 



20 

Frank 48 reports Rhizoctonia violaeea on grapes to be associated 
with Thelephora, which he named Th. rhizoctonige. However, none of 
the above authors have carried on any cultural work to prove the val- 
idity of their claims, hence none of the statements can be accepted 
as valid. 

Rolfs 49 found a basidiomycete associated with Rhizoctonia on 
potato. Pure cultures obtained from spores of the basidiomycete 
always gave a Rhizoctonia, thus proving definitely the relationship of 
the two forms. Rolfs basidiomycete is already known as Corticium 
vagum B. and C. 

American, European and East Indian Hosts Subject to the 
Attacks of Rhizoctonia. 

Name of Host 

Sugar beet Duggar 

bean, pea ' ' ,Leveille 

carrot 

celery 

cotton 

lettuce 

potato " , Leveille, Rolfs. 

crocus Duhamel, Bulliard, Per^. 

asparagus Fougeroux 

alium sp Duby 

lucern Kuhn 

ground nut Shaw 

cowpea ■ " 

jute " 

soy bean " 

mulberry " 

sweet pea Taubenhaus 

Rhizoctonia Attaching Sweet Peas. As far as could be ascer- 
tained no mention could be found in literature of a Rhizoctonia dis- 
ease of sweet peas. I have observed it during winters of 1911 and 
1912 on greenhouse specimens sent in by different sweet pea growers. 
In the fall of 1913, diseased sweet pea seedlings attacked with Rhiz- 
octonia were collected in the greenhouse of the University of Penn- 
sylvania. From correspondence with Plant Pathologists, A. D. Selby 
reports it in Ohio, W. G. Sackett in Colorado and E. C. Stackman in 
Minnesota. There seems no doubt but that the Rhizoctonia root rot 
of sweet pea is much more widespread than is reported. 



21 



Symptoms of the Disease. Severely infected plants have prac- 
tically no root system (Fig. 9) . In less infected plants only one or two 
rootlets may be destroyed. The fungus produces a browning effect of 




H i -- - J 

Fig. 9. Eoot rot caused by Rhizoctonia. (A) healthy. (B) diseased. 



the root before total destruction sets in. In very early stages of infec- 
tion the seedlings are seen to have a wilted appearance ; as the disease 
progresses the infected seedlings fall over and collapse. The fungus 
is not often confined to the roots alone. It is often seen to work its 
way up the stem and this may produce a constricted area which marks 
it off from the healthy part. The fungus being a soil organism, it is 
usually introduced with manure ; infection can take place at any part 



22 

of the roots, or at the stem near the roots. When the latter is the case 
reddish sunken spots are observed at the base of the stein. It seems 
that only young seedlings can be quickly destroyed by the fungus 
whereas older plants seem to linger for considerable time altho such 
plants remain dwarfed, sickly looking and valueless for commercial 
purposes. 

Pathogenicity. The pathogenicity of the sweet pea Rhizoc- 
tonia is readily proven by planting sterilized seeds in sterile soil and 
pots which were inoculated with a pure culture of the fungus. The 
best material to use is somewhat old cultures which have well devel- 
oped sclerotia. It is from the latter that the fungus begins to vegetate 
and to spread in the soil. Five pots were inoculated with the fungus 
and two were kept as checks. The checks germinated and grew well, 
whereas none of the seeds germinated in the infected pots (Fig. 9a). 
In digging out some of these seeds they were found to be invaded with 
the fungus hyphse of the Rhizoctonia. A pure culture may be readily 
obtained from these seeds, thus proving that the Rhizoctonia is a path- 
ogenic organisms. Young seedlings may likewise be infected by the 
fungus, but as already indicated older plants are more resistant as 
they can live for some time with the fungus on them. 

Morphology and Identity of the Sweet Pea Rhizoctonia. So 
far as my studies have gone, only two stages have been found of the 
sweet pea Rhizoctonia. 

1. The Rhizoctonia stage. — This consists of long and narrow 
hyphal branches varying in color from hyalin to reddish brown (Fig. 
10) . These hyphaa are either aerial or are embedded in the substratum, 
varying according to the media on which it is grown. It is this hyphal 
growth which is most active in the parasitism of the fungus. 

2. The Sclerotial stage. — In cultures which are from three to four 
weeks old numerous sclerotia are formed. These sclerotia are made 
up of closely interwoven short barrel-shaped hyphae (Fig. 11). 

According to Shaw 50 Rhizoctonia solani Kuhn produces only mic- 
rosclerotia while Corticium vagum B. and C. produces macrosclerotia. 
After repeated attempts the corticium stage of the sweet pea Rhizoc- 
tonia could not be obtained on artificial media. This accords with the 
findings of Shaw and Rolfs who could not obtain the perfect stage on 
culture media but found it several times on the affected host. How- 
ever, as the sweet pea Rhizoctonia produces macrosclerotia and as 



23 




Fig. 9A. Eoot rot caused by Bhizoctonia. To the right the soil was inoculated 
with the fungus, resulting in no germination. At the left the soil was free from 
the fungus, resulting in good germination. 

already pointed out by Shaw the macrosclerotia produce the Corticium 
stage: the sweet pea organism is therefore referred to as Corticium 
vagum B. and C. 

Pathological Conditions of the Host. The Rhizoctonia fungus 
when attacking other hosts, is known to be confined primarily to the 
cambium layer of the plant. With the sweet pea, conditions are sim- 



24 



ilar. The fungus attacks the phloem of the bundles and makes its way 
into the parenchyma cells as well as to the epidermal cells. The ef- 
fect produced is loss of turgidity, wilting, and early collapse of the 




Fig. 10. Young hyphae of Bhizoctonia from sweet pea. 

Fig. 11. Barrel shaped hyphae from sclerotium of the same fungus. 

host. Infection may take place in the base of stem first and in this 
case the fungus invades both stem and root, or it may start at the roots 
first, then gradually work up to the stem. In either case death of the 
seedling is a natural consequence. In cases where the roots are first 
attacked by the fungus, the former deteriorates so rapidly that when 
pulling out a plant, it is found to be without any root system. 

CHAETOMIUM ROOT ROT, Chaetomium spirochaete Patt. 

Historical In the fall of 1912 Prof. A. C. Beal of Cornell Uni- 
versity sent me specimens of diseased sweet peas grown in the green- 
house for diagnosing the cause of the trouble. The disease was readily 
located in the roots. A fungus was found invading the interior tis- 
sue of the latter but no fruiting stage of any kind could be found 
which would help to identify the fungus. Crush cultures were made 
at once from the diseased tissue, the method employed being the same 



25 

as that described for Thielavia basicola. Some forty poured plates 
of nutrient agar were made in all. In 5 days a pure culture of a 
fungus appeared in all the plates with the exception of one which, 
showed a Fusarium. The cultures were watched closely and in two 
weeks perithecia-like bodies developed in abundance but no spores 
were formed. The fungus proved to be an ascomycete belonging to the 
genus Chaetomium, and determined by Mrs. Flora Patterson as C. 
spirochaete Patt. In mid-winter of that same year, more diseased 
specimens were sent to me from a florist in Illinois. These specimens 
showed the same symptoms as those observed on Prof. Beat's material 
and in this case, too, the trouble was confined to the roots. As pre- 
viously stated, no fruiting stage was found on the affected tissue. 
Cultures made from this material gave a pure growth of Chaetomium 
spirochaete. A search through the literature failed to show the re- 
cord of any of the known Chaetomiums to be parasitic on living plants. 
It is known for instance that C. arachnoides Massee, C. simile Massee, 
C. bostrychoides Zopf and C. murorum Cda., all grow on dung of 
various animals. 

Reinke and Berthold 51 in their studies of the fungous diseases of 
the potato report to have found Chaetomium bostrychoides Zopf and 
C. crispatum Fckl. growing on rotted tubers. The above authors 
state that when germinated spores are placed on a cut surface of a 
healthy tuber they fail to penetrate the same, indicating the sapro- 
phytic nature of the fungus. Its presence on the decayed potatoes 
must have been secondary. The present thesis gives the first record 
of the parasitic nature of Chaetomium. 

Pathogenicity. The fact that a pure culture of C. spirochaete 
was obtained from numerous platings of diseased material obtained 
from two different states at once led to the supposition that the organ- 
ism was the cause of the disease. In order, therefore, to test out the 
pathogenicity of the fungus, the following experiments were tried. 
Out of ten sterilized pots and soil, five were sown with sterilized seeds 
(these were soaked in a solution of formaldehyde, 5 parts in 100 of 
water for one-half hour) inoculated with a pure culture of the fungus 
broken up in sterilized water. In the remaining five pots sterilized 
seeds were sown without the fungus to serve as checks. Both lots of 
seeds germinated and the seedlings of both the inoculated and the 
check pots seemed to grow well for about three weeks. After that time 



26 

the seedlings in the inoculated lots appeared to lose their green color 
and to become paler and yellow. The infected plants could be readily 
pulled out from the soil and the rootlets appeared to be half rotted 
by the fungus, whereas the check seedlings did not exhibit such 
symptoms. Cultures made by surface sterilizing the affected rootlets 
readily gave pure cultures of Chaetomium spirochaete. The experi- 
ment was repeated once more and this time, both checks and inocu- 
lated seedlings were watered frequently, care being taken to keep the 
soil very moist or even wet. This was accomplished by allowing the 
dish to remain filled with water in which the pots stood. In this case 
the checks again remained healthy, but after three weeks the inocu- 
lated seedlings had their roots mostly destroyed by the fungus; the 
infected seedlings could be readily pulled out from the soil. This 
time the greatest part of the root system was destroyed. Cultures 
made from parts of the remaining infected roots readily gave pure 
cultures of the fungus. 

From these experiments it is shown that Chaetomium spirochaete 
altho perhaps a saprophyte will, under certain conditions, assume a 
parasitic nature on sweet peas. It was further shown that in poorly 
drained soils the virulent nature of the organisms becomes more pro- 
nounced. 

Morphology and Physiology of the Fungus. The mycelium of 
the fungus is hyalin, closely septate and branched (Fig. 12) when 
grown in the substratum of the media. The aerial mycelium consists 
of long unbranched filaments and vary in color from very light to 
deep lemon. This seems to be produced within the fungous hyphae 
and later the yellow color is also transmitted to the media in which 
it grows. 

Reinke and Berthold 52 report to have found a conidial stage con- 
nected with C. crispatum. In our work we have as yet not found any 
conidial stage of C. Spirochaete. As previously stated, we have not 
found any fruiting stages of the fungus on the affected host. In pure 
culture in artificial media perithecia appear in two weeks from the 
time of planting and in three weeks mature asci with spores are also 
formed. The perithecia are covered with darkish brown hair-like 
appendages, thus giving it a bristly appearance. The hairs are coiled 
at the apex and septate at different intervals; they are covered with 
very minute pointed warts (Fig. 13). The asci are very evanescent 



27 




Figs. 12-15. Showing (12) mycelium of Chaetomiuni spirochaete. 13, hairs, 
and 15, asci. 16, ascospores. 



14 



and can only be seen in young cultures. In old cultures the ascus 
wall readily breaks so that it is difficult to make out the arrangement 
of the ascospores. There are 8 ascospores to an ascus (Fig. 14-15). 
The ascospores are apiculate (Fig. 16) at both ends. The wall of the 
ascospore is smooth, light brown when young and dark when old. The 
ascospores readily germinate in a sweet pea broth which is made up 
as follows: 

Take 15 grams of ground sweet pea seeds to 1000 cc of water. 
Bring to a boil, filter, then add 15 grams of agar; bring to a boil, 
then filter, tube and sterilize in the autoclave for 15 minutes at 15 
pounds pressure. 



FUSARIUM ROOT ROT, Fusarium lathyri n. sp. 
Historical. It seems that Tulasne 53 was the first to recognize 
the parasitic nature of Fusarium. In 1883 Hansen 54 describes a dis- 
ease on oats which is attributed to Fusarium graminum Corda. In 
1884 "Worthington Smith 55 describes a wheat disease due to Fusispor- 



28 



ium ( Fusarium )'culmorum W. Sm., and another disease on barley due 
to Fusarium hordei W. Sm. In 1889 E. F. Smith 56 mentions different 
related Fusaria isolated from the soil which play the role of plant 
pathogens. The species of the Fusarium are not given. In the same 
year, in their excellent report on the loose smut of wheat, Kellerman 
& Swingle 57 report on a Fusarium which lives as a parasite on the loose 
smut of wheat and which 'they named Fusarium ustilaginis K. & Sw. 
In 1892 Frank 58 reports Fusarium heterosporium Nees, a parasite on 
several graminaceous hosts. In the same year Atkinson 59 reports on a 
cotton disease due to Fusarium vasinfectum. In 1893 Rostrup 60 de- 
scribed an oat disease due to Fusarium avenaceum. In 1899, Smith 61 
describes a disease of cotton, watermelon, cowpeas, and melons as 
due to a Fusarium whose perfect stage was believed to be Neocosmo- 
pora vasinfecta. In 1899 Woods 62 reports on a disease of Chinese 
asters due to a Fusarium. In 1900 Manguin 63 reports on the parasitic 
nature of Fusarium roseum. In 1901 Prillieux and Delacroix 64 report- 
ed on a carnation disease due to F. dianthi. In 1901 Bolley 65 reports 
on a flax disease due to Fusarium lini. In 1901 Sorauer 66 reports on a 
rye disease due to Fusarium nivale. In the same year Pammel 67 re- 
ports on a wheat disease due to Fusarium roseum Lk. In 1902 Smith 68 
reports extensively on a wilt of Chinese Aster the same disease as pre- 
viously reported by Woods 69 . In 1902 Hennings 70 describes a disease 
on the black locust which he attributes to Fusarium vogelii. In 1903 
Van Hall 71 describes a pea disease which he attributes to Fusarium 
vasinfectum Atk. var. Pisi. In 1904 Smith and Swingle 72 reports on 
the dry rot of potatoes due to Fusarium oxysporum. In the same year 
Osterwalder 73 reports on a fruit rot due to F. putrefaciens. In 1905 
Owen 74 reports on a tomato disease which he attributes to Fusarium 
erubescens Appel. and v. Oven. This fungus is claimed to be differ- 
ent from Fusarium solani, F. putrefaciens and F. Lycopersici. In 
1906 Appel and Schikarra 75 report on different species of Fusaria 
which induce disease in plants. In the same year Heald 76 reports 
on a bud rot of carnations due to a species of Fusarium. In 1906 
Hedgcock 7 ' 7 in his extended studies of chromogenic fungi reports 
Fusarium roseum as capable of discoloring wood. In 1907 Chifflot 78 
reports on a pelargonium disease due to Fusarium pelargonii. In 1909 
in their extended studies on corn rots, Burrill and Barrett 79 report on 
three species of Fusaria which attack the ear of corn. In 1910 Wolf 80 
reports on a pansy disease as due to Fusarium. In the same year 



29 

Smith 81 reports on a banana disease due to Fusarium, and Cook 82 re- 
ports on the double blossom due to Fusarium rubi. In 1911 Bubak 83 
describes a rot on ears of corn due to Fusarium maydiperdum. In 
1912 Gifford 84 reports extensively on a damping off disease of con- 
iferous seedlings due to Fusarium, the species not stated. There are of 
course many more Fusaria described, but the aim in this brief his- 
torical sketch is to mention the literature which bears more or less 
directly on the parasitic nature of Fusarium. In a very recent paper 
"Wollenweber 85 describes several species of Fusaria parasitic on the 
potato. He also emphasizes the importance of morphological studies 
as well as infection experiments as the basis of classification in Fusaria. 

Fusarium Boot Rot of Sweet Pea. There is no record in the 
literature of a Fusarium disease of the sweet pea. Several complaints 
from florists have shown that they could not grow sweet peas under 
greenhouse conditions because of a root rot which developed early and 
in some cases destroyed the entire planting. Cultures made from the 
infected material or from the infected soil, and from seedlings sown 
in the laboratory on "the infected soil, gave in each case a pure cul- 
ture of Fusarium. 

Symptoms. The first symptom of the disease is a sudden flag- 
ging of the leaves accompanied by general wilting and collapse of the 
seedling. Usually upon sowing the seeds a fair percentage germinate 
and reach the height of about 8 to 10 inches when they are attacked 
by the fungus. If the collapsed seedlings are allowed to remain on 
the ground, the stems will soon be covered with the sickle shaped 
spores. Eventually the decayed tissue rots and disintegrates and is 
soon invaded by small fruit flies which now begin to distribute the fun- 
gus from place to place by carrying its spores. 

Pathogenicity. The pathogenicity of this fungus is readily 
proven by inoculating with a pure culture of the organism sterilized 
seeds planted in sterile soil. The seed germinate and reach a height of 
7 to 8 inches but soon succumb to the attacks of the fungus. The fun- 
gus can be reisolated from the artificially infected seedlings and the 
disease induced at will (Fig. 17). The checks remain healthy pro- 
vided of course all means of contamination are guarded against. 

Morphology of the Fungus. The mycelium of the fungus is 
hyalin, septate and branched. At an early age the hyphae begin to 



30 




Fig. 17. Fusarium wilt or root rot. At left, healthy; at right, infected. 



form chlamydospores. These are round hyalin bodies often filled 
with oil globules and are formed in the center of the hypha (Fig. 18), 
in this case the contents of the former collect into the chlamydospores. 
Usually also the chlamydospores are born at the tip end of the hyphae 
in chains of twos, threes and even fours (Figs. 19-22). Old cultures 
are practically one mass of chlamydospores. There are also two 
spore forms present and these appear as early as the third day in the 
pure culture. These are microconidia which are fairly abundant and 
macroconidia, varying from two celled to four celled. The average 
form is the three celled. Both micro- and macro- conidia are hyalin 
and smooth (Figs. 23-31). In old cultures the macroconidia shrink 
so that -the septa become slightly pronounced (Figs. 25, 28-29). These 
old macroconidia soon lose their protoplasm or the latter breaks up 



31 



presenting a granular appearance. In young cultures the outer wall 
of the chlamydospore is smooth, but in old cultures it becomes slightly 
warty or covered with minute points (Fig. 19). No perfect stage has 
been found to accompany this fungus either in pure culture or on 
the host. 




Fisrs. 18-31. Fusarium lathvri. showing chlamvdosDores and conidia. 

Identity of the Fungus. There is no doubt but that the fun- 
gus belongs to the genus Fusarium. It produces its micro- and macro- 
spores (sickle shaped) as well as chlamydospores which according to 
Wollenweber 86 are true characteristics of the genus Fusarium. The 
fungus has been grown in pure culture (Fig. 32) and on different 
media for two years and no perfect stage has ever appeared. Unless 
further studies prove differently it seems that the present Fusarium 
is a new species and the name Fusarium lathyri n. sp. is tentatively 
given to it. A description of the fungus follows: 

Sporodochia slightly erumpent to superficial on the host, but not 
always present on culture media. Macroconidia sickle-shaped, slight- 
ly curved and fitting into the section Martiella of Wollenweber, 2 to 
4 septate, the majority being three septate, 15.8x4.2" — 30.8x5. 6 U . 
Microconidia elliptical to oval 9.8x2.8*— 14x3.50^. Chlamydospores 
spherical, thick walled and spinulate when old, 7.3U-9* borne singly or 
in chains of twos, threes and sometimes in fours. 
ROOT ROT OR EEL WORM, Heterodera radicicola (Greef) Muller 

Altho not belonging to the domain of this thesis the eel worm is 
here considered, first because of the important root knot disease it 



32 



produces, and the second, because it opens the way to several fungous 
parasites. 

Heterodera radicicola attacking many hosts. The eel worm is 
of an omnivorous nature. Marcinowski 87 gives a list of 235 species 
of plants affected with the pest. Almost all of the more important 
families of flowering plants are present in the list, as well as one gym- 
nosperm and a fern. The plants include both Monocotyledons and 
dicotyledons, herbs, woody plants, annuals and perennials. Many of 
our garden plants and field crops are attacked by the pest. 

Of the plants said not to be affected by Heterodera, Bessey 88 cites 
the following hosts: Crab grass (Syntherisma sanguinalis), redtop 
(Agrostis alba), Johnson grass (Andropogon halepensis), some varie- 
ties of oats (Avena sativa), Bromus schraderi, Eustachys pe'trea, 




Fisr. 32. Pure culture of Fusarium lathvri. the cause of sweet Dea 

wilt 

some varieties of barley (Hordenm vulgare), perennial rye grass, 
Lolium perenne, Echinochloa frumentacea, Panicum miliaceum, Pen- 
nisteum sp. timothy (Phleum pratense), rye (Secale cereale), Andro- 
pogon sorghum, Triticum, maize (Zea mays), Euchlaena luxurians, 
Bidens leucantha, B. bipinnata, G-naphalium purpurem, Helenium 
tenuifolium, some species of Solidago and Zinnia. 



33 

Heterodera attacking sweet peas. In his excellent work on 
the root knot Bessey 89 mentions the sweet pea as attacked by Heter- 
odera radicicola. Chittenden 90 found the eel worm associated with 
Thielavia root rot. 

In my own investigations I have found the eel worm capable of 
producing the root knot. I have often found this pest to be asso- 
ciated with Rhizoctonia. It seems very probable that the Heterodera 
worm in the case of the sweet pea opens the way to the attacks of 
Rhizoctonia and several other fungi. Heterodera radicicola often 
produces the greatest amount of damage in light sandy soil, but seems 
unable to thrive in heavy clay soils. In every case where seen by the 
writer or where reported by florists and seedsmen the eel worm was 
most troublesome where sweet peas have been grown on too light soils 
in the greenhouse. No sweet peas have been reported to be attacked 
by the eel worm out of doors. 

Symptoms. The disease is characterized by swellings on the 
roots. These are either small swellings formed singly, in pairs, or in 
strings, thus giving the affected root a beaded condition (Fig. 33) or 
the swellings may be very large so as to be mistaken for root nodules. 
However, these galls cannot be mistaken for the normal root nodules, 
because the latter are lobed and are attached at one end (Fig. 34), 
whereas the root gall produces a swelling of the entire surface of the 
part affected. Infected plants usually linger for a long time, but they 
can be distinguished by a thin growth and yellow sickly looking leaves 
and stems. 

B. Diseases of the Aerial Parts of the Plant 

STEM OR COLLAR ROT, Sclerotinia libertiana Fckl. 
Synonomy. 

Sclerotinia libertiana Fckl. 
Peziza sclerotiorum Lib. 
Sclerotinia libertiana Fckl. 

' ' Kauf manniana 
Postuma B. & W. 

" Coemansii Kick. 

" sclerotiorum Br. 

Sclerotinia sclerotiorum Ad. 



34 



History of Sclerotinia libertiana Fckl. as a Plant Disease Pro- 
ducer. In I860 Coemans 91 was the first to record a disease of carrots 
and 'turnip which he attributed to Sclerotinia libertiana (Peziza 
sclerotium). In 1886 De Bary 92 also reports on a disease of turnips 





. .'■ Ir"^£' 





Fig. 

Fig. 



33 . 34 

33. Sweet pea roots affected with eel worm. 

34. Sweet pea nodules formed by nitrogen fixing bacteria. 



and carrots due to S. libertiana. In 1887 Cohn 93 reports on a potato 
disease due to the same fungus. Smith 94 in 1890 reports on a holly- 
hock disease due to Sclerotiana libertiana. In 1891 Behrens 95 reports 
on a hemp disease due to this fungus. In 1892 Humphrey 9G reports 



35 

on a lettuce disease which he thought was due to Botrytis cinerea, the 
then supposed conidial stage of Sclerotinia libertiana. Humphrey 
again in 1893 reports on a cucumber disease due to Sclerotinia lib- 
ertiana. In 1897 Prillieux and Delacroix 97 report on an important 
mulberry disease due to this same fungus. In 1900 in his extended 
studies on Sclerotinia, Smith 98 reports on the omnivorous nature of 
S. libertiana. Hedgcock 99 in 1905 reports on a serious disease of cab- 
bage and cauliflower due to S. libertiana. In the same year Parisot 100 
reports on a disease of Jerusalem artichokes in the western part of 
France and due to this same fungus. He also mentions the potato, 
bean, corn, carrot, turnip, rutabaga and flax as all being subject to the 
same disease. In 1906 Appel and Bruch 101 also report on a similar 
disease of turnip and parsnips. Masseron 102 in 1907 reports this fun- 
gus to produce a serious disease on the garden and field pea. In 1911 
Westerdijk 103 reports a wide range of hosts to be attacked by the fun- 
gus such as rape, cabbage, cauliflower, kohlrabi, sesame, bean, pea, 
vetch, clover, lettuce, Jerusalem artichoke, dahlia, zinnia, sugar beets, 
carrots, turnips, parsnips and beets. 

Sclerotinia libertiana Fckl., a Fungous Disease of the Sweet 
Pea. As far as I could ascertain there is no mention in literature 
of S. libertiana attacking the sweet pea. I have first noticed this dis- 
ease on greenhouse specimens sent in by a grower in Pennsylvania. 
My first record of the disease appeared in the Florist Exchange 104 . 
Observations so far seem to show that the disease is limited to sweet 
peas under greenhouse conditions only. A special effort was made 
to find this disease out of doors but without success. It is well known 
that under certain conditions unfavorable to the host the fungus can 
attack a variety of hosts which grow in the open. That the fungus has 
not been found so far to attack sweet peas out of doors does not limit 
its appearance in the field at any time that climatic conditions are un- 
favorable to the host. 

Symptoms. This is usually a seedling disease (Figs. 35-36) 
altho it may attack plants of all ages (Fig. 36).* And it is most severe 
in poorly ventilated houses or in beds which are overwatered and 
which lack proper drainage. The disease when present does its work 
quickly. Affected plants first show a wilting of the tip and flagging 



*Flgs. 36, 41. Electrotype, Florists' Exchange. Photographs by the author. 



36 

of the leaves and then the seedlings fall over and collapse. The fun- 
gus Sclerotinia libertiana, altho a soil organism cannot attack the roots 
of its host. The fungus penetrates the collar of the stem and complete- 
ly invades the vessels of the host, thus checking the upward flow of the 
water from the roots. Freshly collapsed plants have a watersoaked 









'■B r o 



CO -4J 
CD o 

ft,® 



be 



appearance, later to be overrun with a white weft of fungus mycelium, 
finally to be followed by sclerotia which are found here and there on or 
within the affected stems. 



37 



Pathogenicity. In order to establish definitely the relation- 
ship of the fungus to this disease of sweet peas under glass, sterilized 
seeds were planted in sterilized pots and soil in the laboratory. All 
the seeds germinated and the plants were allowed to grow for three 
weeks, in a perfectly healthy state. Then the pots were divided in 




Fig. S6. Camping off caused by selerotinia. 



two lots ; one lot was left as a check and the other lot was inoculated 
with the pure culture of the Selerotinia by introducing pieces of the 
fungus in the soil. Both lots, check and infected plants, were covered 
with bell jars to imitate the moisture conditions of the greenhouse. 



38 

After four to six days, wilting of the inoculated seedlings began, 
whereas the checks remained healthy. This was repeated several 
times with always the same results. This conclusively shows that the 
fungus Sclerotinia libertiana is able, when present in the soil, to pro- 
duce a disease on sweet peas under glass. The fungus is usually 
brought into the greenhouse with the soil, or with the manure. Cross 
inoculation with the fungus from the sweet pea, lettuce, turnip and 
cucumber on the sweet pea produced typical cases of wilt, thus prov- 
ing conclusively that the fungus from the sweet pea is the same as 
the Sclerotinia libertiana of the hosts mentioned above. 

Identity of the Fungus. The fungus from the sweet pea was 
run on artificial media with parallel cultures of S. libertiana from let- 
tuce, cowpea and cucumber. There was no difference observed in the 
manner of growth nor of sclerotial formation of these strains. Under 
pathogenicity, I have shown that cultures of S. libertiana obtained 
from hosts such as lettuce, turnip and cucumber readily produced 
the typical wilt of the sweet pea similar to that obtained when inocu- 
lations are made with the fungus from the sweet pea on the sweet pea. 
In order to further verify the identity of the fungus, sclerotia from 
cultures three months old were placed in small flat covered chambers 
containing sterile moist sand. These were placed outdoors in the cold 
for four weeks, then brought in the laboratory and kept at room tem- 
perature. The moisture was maintained by adding every three to 
four days some sterile water. In nine weeks the sclerotia germinated 
by sending out from each a number of grayish stalks, and in two 
weeks the apothecia developed at the tip of the stalks. In shape and 
measurement of asci and ascospores the fungus answered in every de- 
scription that of Sclerotinia libertiana. 

Morphology of the Fungus. In my work I find no conidial 
stage of a Botrytis type or of any other type to be connected with 
Sclerotinia libertiana of the sweet pea. This is in accord with the 
studies made by Smith, R. E. 105 . There seems no doubt but that Bot- 
rytis cinerea which is often found to accompany S. libertiana is in no 
way connected with the former. 

POWDERY MILDEW, Erysiphe polygonif 
The sweet pea mildew was first described by Massee 106 as 
being prevalent in England. Erysiphe polygoni was attributed 
as the cause, both of sweet pea mildew and that of the edible 



39 

garden pea, In this country Stewart 107 was the first to record 
a powdery mildew on the sweet pea. However, Stewart did not 
find the perithecial stage, and hence the fungus was not deter- 
mined. The powdery mildew is a very prevalent disease on 




Fig. 37. Anthraenose disease of sweet pea on stem and peduncles. 



40 



greenhouse sweet peas, and on irrigated fields or where they are plant- 
ed on a large scale for seeds. Ordinarily, however, in small garden 
lots, and especially where 'the plants do not receive any water, the dis- 
ease is practically unimportant since the attack is usually very mild 
during the active growing season, but becomes somewhat more abun- 
dant when the plants have passed all usefulness. The writer had the 
opportunity of collecting specimens at random from six large houses, 
and from three acres of out-door sweet peas in Mass. and from 
a similar three acre plantation in Pa. Like Prof. Stewart, the 
writer has only met with the conidial or Oidium stage. On our own 



f :: 


■;V't .'".'' 
* ■ . 









Fig. 38. Anthracnose disease of pods and seeds. 

sweet pea field, we have carefully watched for a perithecial stage but 
without success. Late in the fall, badly infected leaves have been col- 
lected and put away to winter over, but that material up to date, 
April, 1913, has failed to develop perithecia. 






41 



ANTHRACNOSE, Glomerella rufomaculcms (Berk.) 8. & V. Sch. 
A very serious anthracnose disease of the sweet pea on the Dela- 
ware Experiment Station farm was called to the attention of the 
writer during the latter part of July, 1910. This disease proved to be 
the same or very similar to the one reported by Sheldon 10S from West 




V 



Virginia in 1905, and is very probably the so-called "wilt" which 
has been so often referred to in old seed catalogues and treatises on 
sweet peas. 



42 

Symptoms. The disease occurs on the stems, leaves (Fig. 39), 
flowers and pods but is most severe on the latter. There is a general 
wilting of the affected parts followed by dying, which begins at the 
tips of the younger shoots and works downward (Fig. 37). The older 
parts of the plants are not killed immediately but may persist for 
some time after being attacked by the fungus. The dead parts shrivel, 
become brittle, and are soon covered with minute acervuli. The af- 
fected pods are at first a dirty white in appearance but assume a dull 
color, which is due to the presence of the acervuli. A definite canker, 
which is so characteristic of the bean anthracnose is not produced. 
Although the disease on the stems seems to be restricted to the young- 
est growths, the pods may be infected at any stage of their develop- 
ment. The seeds of the diseased pods are always infected, become 
shrivelled and frequently do not reach maturity (Fig. 38.) 

Pathogenicity. Sheldon called attention to the identity of the 
Gloesporium of the sweet pea with Glomerella rufomaculans (Berk.) 
Spauld. & von Sch. which is the cause of the bitter rot of the apple. 
With this in mind, the writer made the following experiments in the 
autumn of 1910. Sweet pea seeds, which to all appearances were per- 
fectly healthy, were carefully selected, sterilized by immersion for 15 
minutes in a 5% solution of formaldehyde, and planted in pots in 
soil which had been sterilized by heating for one hour in the autoclave. 
The seeds germinated in 5 days and the seedlings were allowed to 
grow for three weeks. Fifty plants were allowed to grow in each pot. 
The temperature of the room ranged as high as 72° F. during the day 
and several degrees lower during the night, but not low enough to 
injure the plants. All the seedlings grew well and were perfectly 
healthy. The day before inoculation the pots with the seedlings were 
covered with bell jars thus forming moist chambers. These covers 
were removed one day after inoculation. Two methods of inoculation 
were employed: (1) the introduction of spores into the living stems 
through punctures made with a sterilized needle; (2) by liberally 
spraying the surface of the plants by means of an atomizer with 
spores suspended in sterilized water. Fruits of apples and pears on 
the trees in the orchard were also treated in the following manner: 
Healthy fruits on the trees were first washed with a 5% solution of 
formaldehyde and then rinsed with distilled water. They were then 
inoculated through sterile needle punctures and covered with paper 
bags. For the inoculation, pure cultures were used of G-loeosporiums 



43 



The results of these experi- 



from various sources as indicated below, 
ments are given in Table I. 

The data in Table I show: (1) that the original organism of the 
sweet pea is pathogenic to tfre sweet pea, and also to the apple in which 

TABLE I 



Source of 
€ Gloeospor- 
iurn culture 


Number and kiud 
of plants 
inoculated 


Method of 
-inoculation 


Date of 
inocula- 
tion 


Results of 
inoculation 


Checks 




50 sweet pea seed- 
















Sweet Pea 


lings, 3 weeks old 


Punct: - e 


Sept. 


26 


Oct. 


2, all dead 




50 all 


it it 


Same 


Atomizt 


Oct. 


26 


Nov. 


7, " " 




healthy 


it it 


Same 


1 1 


JNTov. 


14 


Nov. 


21, " " 




t * 


Apple 


Same 


Puncture 


Oct. 


10 


Oct. 


18, " " 




a 


1 1 


50 sweet pea seed- 


i i 


1 1 


1 1 


Oct. 


22, " " 








lings 4 weeks old 










1 1 


1 1 


Same 


Atomizer 


Nov. 


20 


Nov. 


29,44 " 




tt 


it 


Same 


Puncture 


Oct. 


26 


Nov. 


1,31 " 




1 1 


1 1 


Same 


' ' 


Nov. 


14 


Nov. 


20, all ' ' 




tt 


1 1 


Same 


Atomizer 


Oct. 


5 


Oct. 


14,37 " 




a 


1 1 


50 sweet pea seed- 
lings 8 weeks old 


1 1 


Oct. 


7 


Oct. 


17, 42 ' ' 




1 1 


Sweet Pea 


12 apples on tree 


Puncture 


Oct. 


7 


Oct. 17, typical 
bitter rot 


5 


1 1 


it tt 


16 " " 


1 1 


Oct. 


8 


1 1 


it a 


12 


1 1 


Apple 


15 " " 


1 1 


1 1 


< c 


1 1 


tt it 


16 


1 1 


1 1 


21 pears on tree 


1 1 


1 1 


1 1 


i t 


ti it 


8 


■ 1 1 


Sweet Pea 


18 " " 


1 1 


' ' 


1 1 


1 1 


1 1 tt 


11 


1 1 


tt ti 


16 " " 


1 1 


1 1 


1 1 


1 1 


it i i 


12 


1 1 



it causes the typical bitter rot; (2) that Gloeosporium fructigenum 
Berk, from the apple causes a disease on the sweet pea which is sim- 
ilar to the disease caused by the original sweet pea Gloeosporium. 
This definitely proves that Glomerella rufomaculans (Berk.) Spauld. 
& von Sch. is the cause of the anthracnose disease of the sweet pea. 

Relation of other Gloeosporiums to the Sweet Pea Disease. 
"While working on the question of the identity of the bitter rot of the 
apple and the anthracnose of the sweet pea, it was considered desir- 
able to determine whether other species of Gloeosporiums could pro- 
duce an anthracnose of the sweet pea similar to that caused by the 
bitter rot organisms of 'the apple. Therefore, sweet pea seedlings were 
inoculated with spores from pure cultures of five different GloeoV 
sporiums then in stock in the laboratory. The results of these experi- 
ments are given in Table II. 



TABLE II 





Number and 




Date of I 


[ 


Species of 


kind of plants 


Method of 


inocula- Resulted 


Check 


Gloeosporium 


inoculated 


inoculation 


ti on inoculation 




Gloeosporium 


50 sweet pea 


Puncture 


Oct. 26 


Nov. 7, 42 


50 all healthy 


gailarum 


seedlings 






dead 




1 1 


1 1 


i c 


Nov. 14 


Nov. 25, 41 
dead 




i i 


1 1 


Atomizer 


Nov. 30 


Dec. 12, 8 
dead 




1 1 


i i 


i i 


Dec. 2 


Dec. 14, 19 
dead 




1 1 


1 1 


i i 


Oct. 26 


Nov. 7, 34 
dead 




Gloeosporium 


< i 


Puncture 


Nov. 14 


Nov. 25, 43 




officinale 






'■'■< 


dead 




1 1 


( i 


1 1 


Nov. 30 


Dec. 12, 50 

dead 




1 1 


1 1 


Atomizer 


Dec. 2 


Dee. 14, 50 
dead 






1 1 


t i 


Oct. 26 


Nov. 7, 50 
dead 




Species from 


t( 


Puncture 


Nov. 14 


Nov. 26, 42 




May apple 








dead 




< i 


n 


i i 


Nov. 30 


Dec. 12, 17 
dead 




i t 


n 


Atomizer 


Dec. 2 


Dec. 14, 19 
dead 




t i 


it 


< < 


Dec. 26 


1 1 




Glomerella 


it 


Puncture 


1 1 


Nov. 20 




psidii 


(( 


Atomizer 


1 1 


failure 

1 1 




Species from 


(t 


1 1 


Oct. 20 


i c 




Persea 












t i 


1 1 


Puncture 


1 1 


t i 




Gloeosporium 


15 pears on 


1 1 


t i 


Nov. 15, typ- 


7 " 


gailarum 


tree 






ical bitter rot 




Gloeosporium 


12 


i t 


1 1 


i i 


5 " 


Officinale 












Species from 


14 " 


1 1 


i i 


i i 


9 " 


May apple 








Nov. 15, not 




Glomerella 


19 " 


1 1 


1 1 


typical bitter 


6 " 


psidii 








rot 




Species from 


16 '.' 


i t 


Oct. 5 


' ' 


6 " 


Persea 












Species from 


106 pole lima 


1 1 


Oct. 7 


Oct. 19, suc- 


16 " 


sweet pea 


on pods 






cessful 




Species from 


66 " 


1 1 


" 


1 1 


12 " 


apple 












Species from 


24 " 


i i 


i i 


1 1 


9 " 


May apple 












Gloeosporium 


32 " 


i i 


" 


1 1 




Officinale 












Gloeosporium 


42 " 


1 1 


c c 


it 




gailarum 












Glomerella 


60 bush lima 


C I 


t i 


1 1 




psidii 


bean 










Species from 


42 " 


1 1 


<< 


i i 


19 " 


sweet pea 












Species from 


49 " 


I I 


1 1 


i i 


12 " 


apple 












Species from 


40 " 


Atomizer 


" 


Oct. 26, fail- 


12 " 


apple 








ure 




Species from 


58 " 


1 1 


" 


i i 


32 " 


sweet pea 













45 

From Table II it will be seen that the Gloeosporium from the May 
apple fruit (Podophyllum peltatum), G. gallarum Ch. Rich, from oak 
gall, and G. officinale E. & E. from sassafras leaves, are able to infect 
sweet pea seedlings through puncture inoculations as readily as the 
sweet pea or the apple Gloeosporium. Furthermore, that G. officinale 
readily infects sweet pea seedlings by atomizer inoculations, the infec- 
tion being nearly 100%.. While G. gallarum and the species of Gloeo- 
sporium from the May apple fruit also infect sweet pea seedlings, the 
percentage of successfully inoculated seedlings is smaller with the 
atomizer inoculations than when the inoculations are made by needle 
punctures. 

Glomerella psidii (G. Del.)' Sheldon and the Gloeosporium from 
Persea failed to infect sweet pea seedlings. 

The apple trees in the old orchard of the Experiment Station did 
not bear enough fruits to permit inoculation experiments with the 
above five organisms ; hence Kieffer pear trees which bore heavily were 
chosen for this purpose. They were accordingly inoculated with the 
five Gloeosporiums already mentioned. The results of these inocula- 
tions (Table II), show that the species of Gloeosporium from the May 
apple G. gallarum and G. officinale produce the typical bitter rot on 
the pear, while the Gloeosporium from the guava and Persea infect 
the pear, but cause dull spots in which the acervuli are black and the 
spores are borne on long black conidiophores. Similar results were 
obtained when pear fruits were inoculated with the same Gloeosporium 
and kept in moist chambers in the laboratory. These experiments 
also show (Table II) that all the Gloeosporiums here considered, ex- 
cept the species from guava and Persea very readily produced an 
anthracnose disease on the pods of the lima beans in the field, which 
was similar to the anthracnose of the sweet pea, but quite unlike the 
bean anthracnose, Collet otrichum lindemuthianum (Sacc. & Mag.) B. 
& C. All the Gloeosporiums referred to above attacked the pods of 
the lima beans in the field when the inoculations were made by means 
of punctures, but not otherwise. The spots produced on the lima bean 
pods by Glomerella psidii are gray with grayish acervuli and made up 
of black setae very similar to those of a true Colletotrichum, but un- 
like C. lindemuthianum. None of the above species of Gloeosporiums 
would infect bean or vetch seedlings. The same precautions were 
taken in inoculating the bean pods and pears in the field as with the 
apples. 



46 

Further Studies of some Oloeosporiums and their relation to the 
Sweet Pea Anthracnose. The first year (1910) the inoculations were 
carried on at a time when both the apples and the pears were almost 
mature, and ripe fruits being a more favorable medium, since they are 
physiologically less active than young ones, it was felt advisable to 
start the present inoculations of the apples and pears in the orchard 
at a much earlier date, this time using more organisms. The inocula- 
tions were begun in 1911 when the fruits were the size of a grape, and 
were repeated at various stages of their development. The Kieffer 
pear and the Rubicon and Paradise Sweet apples were selected for 
this purpose. The inoculations were made by means of punctures 
through the cuticle. For each organism a different sterilized needle 
was used. Natural infection of the inoculated fruits was prevented 
by means of heavy paper bags which were tied to the limbs to which 
the inoculated fruits were attached. Any inoculated fruits which 
happened to drop off fell into the bags and were retained there. In 
every case where infection occurred it first appeared at the point of 
inoculation. For each organism eight fruits were used as checks. 
These were punctured with a sterile needle and covered with paper 
bags, and in all cases remained healthy. Investigations were also car- 
ried on with sweet pea, specimens of which were grown in the labor- 
atory from carefully selected and sterilized seeds grown in sterilized 
pots and soil. Checks were also used, fifty seedlings for each organism, 
and these in all cases remained healthy, although they were punctured 
with a sterilized needle. Only spores from pure cultures were used 
for the inoculations. The results obtained are given in Table III. 

From Table III it will be seen that Glom. rufomaculans from 
apple and sweet pea, Gloe. gallarum Ch. Rich., Glom. gossypii (South) 
Edg., Gloe. diospyri E. & E., Colletotrichiim phomoides (Sacc.) 
Chest., and C. nigrum Ell. & Halst. produce the typical anthracnose 
disease on the sweet pea and the symptoms produced by all the above 
organisms were identical with those produced by the original Gloeo- 
sporium isolated from diseased sweet pea plants in the field. Many 
more inoculations than are indicated in Table IV were made with the 
above named organisms on the sweet pea. They were omitted from 
the table, since the results obtained were similar to those given above. 
The data in Table III further show that Gloe. piperatum E. & E. 
failed to infect the sweet pea by atomizer inoculation, while infection 
by puncture inoculation was fairly successful. When this organisms 



47 



was reisolated from seedlings infected by puncture, it regained its 
virulence, and then became able to infect sweet pea seedlings by atom- 
izer inoculation. Glom. rufomaculans from the fig failed to infect the 
sweet pea, and, as will be seen later, it also failed to infect apples and 

TABLE III 



Species of 


Methods of 


Date of 




Results of 


fungus 


inoculation 


Inoculation 


inoculation 


Glomerella rufomaculans 














Atomizer 


June 16 


June 28, 


99% infection 


Glom. rufomaculans 














1 1 


May 21 


June 2, 


92% 


< i 


i i 


1 1 


May 25 


June 6, 


90% 


(i 


C I 


c i 


June 16 


June 21, 


95% 


1 1 


I ( 


1 1 


June 29 


July 11, 


41% 


i i 


( c 


c I 


July 27 


Aug. 10, 


80% 


1 1 


i c 


1 1 


Nov. 1 


Nov. 10, 


100% 


1 1 


Gloeosporium gallarum 


1 1 


June 16 


June 28, 


91% 


1 1 




I c 


May 25 


June 12, 


no 


cc 


< i 


Puncture 


i i 


June 12, 


2% 


c e 


t < 


i i 


June 29 


July 6, 


41% 


i i 


< < 


Atomizer 


June 4 


June 21, 


no 


c t 


it * 


t { 


July 27 


Aug. 9, 


50% 


1 1 




i c 


May 21 


June 2, 


82% 


1 1 






1 1 


I c 


May 25 


June 12, 


60% 


l c 


i c 


( I 


June 21 


July 7, 


100% 


1 1 


t c 


( i 


June 29 


July 7, 


80% 


c c 




i i 


Oct. 28 


Nov. 10, 


82% 


1 1 


Colletotrihum phomoides 


( i 


1 1 


Nov. 10, 


80% 


1 1 




I i 


l c 


Nov. 10 


92% 
no 


t i 


C. gloeosporioides 


c t 


July 3 


July 14, 


1 1 


tt 


Puncture 


Aug. 1 


Aug. 10, 




1 1 


Glom. rufomaculans 
















May 21 


June 2, 




( i 


i e 


Atomizer 


<< 


June 2, 




c t 


Gloeosporium from 

Populns deltoides 


1 1 


June 29 


July 11, 




1 1 


1 1 


Puncture 


May 25 


June 12, 




( i 


C. lindemuthianum 


1 1 


Aug. 1 


Aug. 10, 




{ I 


1 1 


Atomizer 


< i 


Aug. 10, 




1 1 


Gloe. musarum 


1 1 


July 27 


Aug. 10, 




1 1 


i i 


Puncture 


< i 


Aug. 10, 




C I 


C. lagenarium 


n 


Nov. 1 


Nov. 10, 




1 1 


1 1 


Atomizer 


« i 


Nov. 10, 




i I 



pears on the tree. Edgerton 109 states that the above two organisms 
readily lose their virulence when grown for some time on artificial 
media. The Gloeosporium sp. from Populus deltoides, Collet otrickum 
lindemuthianum (Sacc. & Magn.) B. & C, and Gloe. musarum Cke. 



*Gloeosporium piperatum reisolated from sweet pea seedlings infected by 
puncture inoculation. 



48 



& Mass. failed to infect the sweet pea after repeated trials both by 
puncture and atomizer inoculations. In comparing Tables I and II 
we see that the organisms which infect the sweet pea also infect the 
apple, with the exception, however, of Gloe. gossypii, which readily 
infects the sweet pea by atomizer inoculation, but always fails to infect 
apples on the tree. 




Fig. 40. Bitter rot of apple induced by the same fungous which causes anthrac- 
nose of the sweet pea, viz. — Glomerella rufomaculans. 

The data in Table IV show that none of the organisms used could 
infect the Rubicon apple on the tree when the fruits were about the 
size of a large grape. Later, however, by June 26, the first positive 
infection was obtained with Glom. rufomaculans from the apple. At 
this same date all the other organisms used failed to infect. On July 
15 the same condition prevailed. By August 19, typical bitter rot 
infections were obtained with Glom. rufomaculans from the apple and 
sweet pea, Gloe. officinale, Gloe. gallarum, Gloeosporium sp. from 
May apple fruit, and Gloe. piperatum. Negative results were obtained 
with Glom. rufomaculans from fig, Glom. gossypii, Gloeosporium sp. 
from Populus deltoides, Colletotrichum lindemuthianum and Gloe. 



49 



musarum. Further inoculations were made on the Rubicon apple 
until September when the fruits were ripe and the results were the 
same as mentioned above. 

Field inoculations were tried on the Paradise Sweet apple with 
the organisms mentioned in Table IV and with like intervals of time 
between them. The results obtained were the same as with the Rubi- 
con except that positive infection with Glom. rufomaculans from 
apple was not obtained before Sept. 7. Inasmuch as the Paradise 
Sweet is a late variety this indicates the greater resistance of late 
over early varieties. 





TABLE IV 






Species of 


No. fruits 


Dates of 




Results from 


fungus 


inoculated 


inoculation 




inoculation 


12 species named below 


6 fruits 
for each 
organism 


June 2 


June 12 


all healthy 


12 species named below 


i i 


June 6 


June 21 


all healthy 


Glomerella rufomaculans 










from apple 


8 


June 14 


June 26 


all typical bitter rot 


11 other species named 










below 


8 


1 1 


" 


all healthy 


Glom. rufomaculans 










from apple 


8 


June 27 


June 15 


all typical bitter -rot 


Glom. rufomaculans 










from sweet pea 


10 


< i 


< i 


8 fruits show small spots 


Gloeosporium from 






i i 


2 fruits are healthy 


May-apple 


10 


1 1 


1 1 


same as above 


9 other species named 








below 


10 fruits 


' ' 


i i 


all healthy 




for each 








organism 








Glom. rufomaculans 










from apple 


8 


July 7 


Aug. 2 


all typical bitter rot 


Glom. rufomaculans 










from sweet pea 


10 




i i 


1 1 


Gloeosporium officinale 


10 




l c 


" 


Gloe. gallarum 


10 




1 1 


'• 


Gloeosporium sp. from 






1 1 


t i 


May apple 


10 




1 1 


i i 


Colletotriehum phomoides 


10 




I I 


all very small spots, but 


Gloe. piperatum 


10 






typical bitter rot 
very small spots but not 


C. gloeosporioides 


10 




I i 


Glom. gossypii 


10 






typical bitter rot 


Gloeosporium sp. from 






1 1 


same as above 




10 




( i 


all healthy 


C. lindemuthianum 


10 




i t 


1 1 


C. lagenarium 


10 




i i 


i c 



50 

Field inoculations were also carried on with Kieffer pear fruits. 
The latter being a variety which ripens very late, positive infection 
on the fruit with six of the organisms could not be obtained earlier 
than Oct. 6. The above fungi which produce 'the anthracnose disease 
of the sweet pea and the bitter rot on the apple also produce typical 
bitter rot on the Kieffer pear. 

The foregoing experiments have conclusively proved that the an- 
thracnose disease of the sweet pea is identical with Glom. rufomaculans 
which produces the bitter rot of the apple. Moreover, the six organ- 
isms above mentioned, which were previously considered as distinct 
species, are now shown 'through the above experiments to be identical 
with Glom. rufomaculans, since they readily produce the typical an- 
thracnose disease on the sweet pea and the bitter rot of the apple and 
the pear fruits on the tree. The experiments further indicate the 
saprophytic nature of Glom. rufomaculans 110 since no infection could 
be obtained on very young apples or Kieffer pear fruits on the tree. 
In the Delaware bulletin just referred to an explanation is given of 
'the causes of the difference in resistance between different varities 
of the same fruits and between young and older fruits of the same 
variety. If we look for an explanation as to why Glom. gossypii in- 
fects sweet peas and fails to infect apples and pears on 'the tree but 
readily infects the same fruits when they are picked and placed in 
moist chambers in the laboratory, we are brought to the following 
theory: It seems that the Glom. gossypii at one time was identical 
with Glom. rufomaculans, but that through long association with the 
cotton plant it has become so modified in its habits as to make it a phy- 
siological species capable of infecting the sweet pea and possibly other 
hosts, but having lost the power to infect the apple. From this it 
would seem that it is the cell contents of the host which may in some 
cases modify the physiological habits of an organism. To refute the 
above statement it could not be argued that the sweet pea can be in- 
fected by all species of Gloeosporium. This is not the case, since 
experiments have proven that only the organisms which infect the 
apple can also infect the sweet pea, with the above exception. 

The writer hopes 'to continue experiments along these same lines 
with the object of finding out whether certain other supposedly differ- 
ent species of the Glomerella type are not one and the same. 

Mode of Infection and Period of Incubation. The anthrac- 
nose of the sweet pea is mainly a disease of the tender parts of the 



51 

plant. Infection starts at the tips and the fungus works downwards 
invading both stems and leaflets until it reaches a node on the older 
parts of the stem, where it is stopped in its course. It is not infre- 
quent, however, to find whole branches dying, and sometimes the 
entire plant is involved. In such cases it has been found that the 
plant is suffering from insect attacks, either by plant aphids (Aphis 
sp.), or more especially the red spider, (Tetranychus bimaculatus 
Haw.). These help the fungus both by weakening the host plant and 
by distributing the spores over its surface. The spores when ger- 
minating have no difficulty in penetrating the oldest parts of the host 
if it has been punctured by these insects. This explains why the 
plants suffer most during the hot dry weather, since at that time the 
aphids are most abundant. Infection often begins with the blossoms 
at the junction between the flower and the peduncle, in which case 
the blossom shrivels. The pods, also, even those which are nearly ripe, 
are often seen to be badly affected. Here, too, the aphids will be found 
to have opened the way for the fungus. These symptoms are observed 
in the field when infection takes place naturally, or in the laboratory 
where the plants are artificially inoculated with Glom. rufomaculans 
from the sweet pea. The same mode of infection and the same symp- 
toms are observed with the other organisms which are capable of in- 
fecting the sweet pea. 

The spores of Glom. rufomaculans from the sweet pea usually 
germinate in from six to twenty-four hours, according to the amount 
of moisture in the atmosphere. The germ tubes enter the host by 
breaking through the epidermal cells of either leaf or stem. In case 
the spore lodges on a stomate, the germ tube grows away and avoids 
entrance. It may be that the gases which are given off at the stomates 
are toxic and prohibit the entrance of the germ tube, which often 
breaks through the epidermal cells as soon as the spore germinates. 
At other times the spore germinates by sending out a short germ tube 
which forms an appressorium which attaches to the epidermal wall. 
This appressorium is then seen to germinate, its germ tube breaking 
through the epidermal cell. 

The period of incubation varies from three to five days according 
to the amount of moisture in the atmosphere. The acervuli appear 
within five days after wilting begins unless the weather is dry, when 
they may not appear until eight to ten days after infection. In the 
field the sweet pea anthracnose is at its height during July and Aug- 



52 

ust. This is also the time when the bitter rot of the apple makes its 
appearance in the orchard. It is thus easy to understand how readily 
the natural cross inoculation may be effected. 

Morphology of the fungus. The spores and mycelium of the 
Gloeosporium of the sweet pea do not differ from the corresponding 
structures of Glomerella rufomaculans.. Sheldon first observed endo- 
spores of the Gloeosporium of the sweet pea in pure cultures, and the 
writer has observed the same structures in hanging drop and plate 
cultures of Glomerella rufomaculans from the apple and the sweet 
pea, G. officinale and G. psidii. 

The formation of endospores is as follows : In some of the mycelial 
threads the protoplasmic content rounds itself into one or more cells, 
resembling chlamydospores. At the tip end of these cells a filament 
grows out within the empty part of the mycelial thread and at the 
tip of this filament the endospore is formed in the same manner as the 
conidia on the conidiophores of a Gloeosporium. The endospore is 
broken off and pushed forward for the formation of a new one. Fur- 
ther studies are necessary to determine the conditions necessary for 
endospore formation. The spores of G. fructigenum, G. Gallarum, 
and the Gloeosporiums from sweet pea and May apple, all germinate 
in the same manner, by sending out a stout germ tube. On five dif- 
ferent synthetic media these Gloeosporiums produce growths and 
fructifications of the same character. The spores of the species from 
guava and Persea germinate by sending out a very thin germ tube. 
They also differ in manner of growth and fructification on the syn- 
thetic media from the other organisms used. Until the perfect stages 
are found, it appears from these studies that we are justified in con- 
sidering G. gallarum, G. officinale and the Gloeosporium from the 
May apple fruit as one and the same with Glomerella rufomaculans 
(Berk.) Spaul. & von Sch. of the apple and the sweet pea. 

Life History. In order to determine whether the disease is 
carried over with the seeds of the sweet pea, a large quantity of dis- 
eased pods were collected and kept over winter, some in the laboratory 
and some out of doors. Spores from both lots of materials were tested 
Nov. 22, Dec. 22, 1910, Jan. 22, Feb. 22, March 15, 20, 24, April 20, 
May 21, and June 20, 1911. In all cases the spores germinated well 
and produced normal colonies on bean agar. Spores of cultures ob- 
tained from the sowing of June 20, 1911, readily infected healthy 



53 

sweet pea seedlings, wnich were grown in pots in the laboratory. This 
indicates that the organism is carried over the winter as viable spores 
on the pods and on the seeds, and there is very little doubt that the 
disease is introduced into new localities through diseased seeds. 

MOSAIC DISEASE OF THE SWEET PEA 

Brief History. The first study of the disease was made by 
Mayer in in 1866 on the mosaic of tobacco. Mayer found that the dis- 
ease was not induced by insufficient mineral nutrients. He also found 
the disease to be distributed over large areas irrespective of soil con- 
ditions and further proved that the juice of the leaves of affected 
plants, when injected into healthy leaves would reproduce the disease 
in from ten to eleven days. Mayer found that a temperature of 60° 
C. does not destroy the infectious nature of the juice, but that a tem- 
perature of 80° kills it. Mayer could not find any animal or fungus 
parasite to be associated with the disease, altho he believed the true 
cause to be bacteria which could not be isolated. 

In 1892 Iwanowsky 112 confirmed Mayer's work. He too was un- 
able to isolate the specific germ on artificial media but states that he 
saw the bacteria and proved their presence in the tissues of the affect- 
ed host. In 1894 Prillieux and Delacroix 113 found this same disease 
on tobacco in France. 

In 1897 Marchal 114 described under the name of "La mosaique 
du tabac" a disease similar in appearance to that described by 
Mayer 115 . Marchal claims to have obtained from diseased leaves a 
motile bacillus forming chains in culture media, and capable of re- 
producing the disease by inoculating with a pure culture. 

In 1898 Beijerinck added considerable to our knowledge of this 
disease. He apparently proved the absence of bacteria in the devel- 
opment of the disease. When the juice of diseased plants is passed 
through filters, the liquid, while remaining perfectly clear and free 
from bacteria still retains the power of infection. He found that only 
growing meristematic tissue could become diseased. Among many 
other things he also found that soil from diseased plants may infect 
healthy plants. He further showed that the infective material could 
be transported through considerable distance without losing its vir- 
ulence. He assumed the virus to be a non-corpuscular fluid like mate- 
rial which has the power of growth when in contact in a sort of sym- 



54 

biosis with growing cells. He called it therefore "a living fluid con- 
tagium. ' ' 

In 1902 Woods 116 concludes that 'the disease is due to the presence 
of oxidizing enzymes in the plant; these he designated as oxidase and 
peroxidase. 

In 1904 Selby 117 refers to the mosaic disease of tobacco as a non- 
parasitic disease, he, accepting the conclusions of Sturgis and 
Woods. 

In a recent paper, Allard 118 has succeeded to transfer by means 
of inoculation the mosaic of tobacco to other solanaceous plants of the 
following genera : Nicotiana, Lycopersicum, Petunia, Physalis, Datura, 
Hyoseyamus, Solanum and Capsicum. T. Allard also found aphids 
to be carriers of the disease. 

Mosaic Disease of the Sweet Pea. As far as known there is 
no mention made before of the mosaic disease of the sweet pea. The 
writer first made a study of the disease in the summer of 1912 and his 
first published report appeared in the Florist Exchange 119 . 

Like the anthracnose, the mosaic of the sweet pea is a very impor- 
tant disease. Both oat door and greenhouse plants are alike sub- 
ject to it. 

Symptoms. Mosaic is readily distinguishable by a yellow dotting 
or mottling of the leaf, presenting in some instances a beautiful mosaic 
structure, hence its name (Fig. 41). Affected leaves seem to linger 
for a time but 'they eventually lose all their chorophyll and soon drop 
off. Another symptom of this disease is a curling of leaves (Fig. 42), 
resembling the curling induced by the green aphids, but in this case the 
aphids had no association with it. The disease makes its appear- 
ance after the seedlings are from three to four weeks old. Often, the 
disease is so bad and the curling so pronounced that the plants thus 
affected cannot make any headway and remain dwarfed. An attempt 
is made by these curled parts to produce a few flowers, but the later 
are borne on very short peduncles as compared with the long ped- 
uncles of healthy plants of the same variety. Frequently, however, 
the affected plants outgrow the disease entirely, and thus a distinct 
line of demarcation is observed between the previously diseased part 
and the healthy part of the new growth. At other times infected 
plants keep en growing and even flowering, with the disease keeping 
pace. 



55 




Pathogenicity. Like peach yellows and mosaic disease of tobacco 
and tomato, this disease of the sweet pea, too, can be reproduced 
by a puncture with a sterile needle from the diseased leaf into 



56 



a healthy leaf. No organism could be obtained in culture, nor 
could it be detected with the microscope. Nevertheless, this disease 
is contagious, as is the peach yellows. When the disease first made 
its appearance in our experimental sweet pea field, the diseased areas 




Fig. 41 Mosaic disease causing dwarfing of the plant and rolling of the leaves. 



01 



were immediately located in order to learn something of its spread. 
They formed two small areas, one in about the center of the field, the 
other in the southeast corner. Within ten days another survey was 
made and the whole field was found to be infected. With the excep- 
tion of the dwarf Cupid varieties, which are seemingly immune, all 
the rest were found to be affected with the mosaic. When first inves- 
tigating this disease I thought that, perhaps, this mottling of the 
leaves was merely a variegated condition. We also thought that per- 
haps the curling of the tender tips as well as the mosaic effect was due 
primarily to 'the presence of aphids, which at the beginning of the 
season were so plentiful. Experiments were then undertaken to de- 
termine definitely these points. Accordingly, sterile pots with sterile 
soil were isolated in a glass chamber and the plants were allowed to 
grow for three weeks to see if any disease would develop on them. 
However, these plants remained very free from any disease. The pots 
with plants were then divided into four lots ; into Lot I were intro- 
duced a few stem mothers of aphids from affected mosaic plants in 
the field. In Lot II were introduced a few stem mother aphids from 
apparently healty plants in the field. The plants in Lot III were 
punctured with sterile needles and by pricking a mosaic affected leaf, 
and then puncturing with the same needle the healthy leaves. Lot 
IV was punctured merely with the sterile needle, the plants of this 
lot were designed to serve as checks. In each lot there were two pots 
with plants in order to duplicate each experiment. After ten days 
the lot which were inoculated with the aphids from the diseased and 
healthy plants both began to show the symptoms of mosaic. This, 
therefore, would appear to show that the mere puncture of aphids 
would be responsible for the mosaic disease. However, this is not the 
case, as we will soon see. Moreover, it is easy to suppose, and that on 
very good ground, that the aphids taken from seemingly healthy plants 
in an infected field might themselves have been infected before. But 
this would be no valid proof. Lot III, which was infected with needle 
punctures from diseased leaves, began after ten days to show the 
mosaic disease, while the check punctures remained all healthy to the 
end of the experiment. This definitely proves that the aphids are not 
the cause of the trouble but are merely the carriers of the mosaic dis- 
ease. It seems, therefore, that any steps taken to control the aphids 
may also serve to control the mosaic. From this, too, it is evident 



58 

that not only the aphids, but also any biting or sucking insect may 
help spread the disease. 

It has been definitely proven that the mosaic disease is contagious, 
since it can be produced at will by artificial inoculations. The symp- 
toms produced in artificially inoculated plants are similar to those in 
the field, namely, a yellowish spotting or mottling of the leaves and 
a tendency of the leaves of the tips of the plant to curl. 

Cause of the Mosaic Disease. Mention has been made of pre- 
vious workers who with ourselves have definitely proven the infectious 
nature of the disease. Attempts to prove the cause of the trouble 
have resulted in failure. Mayer 120 failed to find the association of ani- 
mal or fungus parasites with the disease. He thought that bacteria 
were the cause of the disease, but all inoculations with bacteria culti- 
vated from the surface of diseased leaves, and with mixtures of dif- 
ferent bacteria gave negative results. 

Beijerinck 121 disproved the theory that the cause of the trouble 
was bacteria, by showing that the juice of diseased plants filtered 
.through Chamberland filters while remaining perfectly clear and free 
from bacteria still retained the power 'of infection. 

Sturgis 122 in his conclusions states as follows : 

"It (mosaic) is not caused by predaceous insects, nematodes, or 
parasitic fungi. 

"Bacteria have not been associated with the disease but no crit- 
ical method for their isolation or culture has been applied, and there- 
fore the question of their influence cannot at present be answered. 

Woods 123 believes the disease to be of a physiological nature and 
of enzymic activity. Woods claims to have reproduced the disease 
several times by merely removing the tip of a rapidly growing plant. 

Suzuki 124 in his studies of the so-called mulberry dwarf troubles 
in Japan (all evidence seems to show that this disease is of a similar 
nature as our mosaic), concludes that the principal cause of the dis- 
ease is due to the practice of subjecting the mulberry trees to repeated 
low cuttings, thus removing the reserved food which is required for 
growth. Woods believes that it was the enzyme (peroxidase) of the 
leaves that induced the disease because he claims that he induced the 
disease artificially by injecting into a healthy plant the juice from 
another healthy plant. Woods found more peroxidase in diseased 
than in healthy plants. "It is through the introduction of the enzyme 



59 

into the infected host that pathological changes are brought about 
which result in an increase of the normal enzymes of the cell and the 
decrease of available reserve food. When this condition is reached, 
it is very difficult for the plant to outgrow the trouble/' Accepting 
this hypothesis, "Woods is at a loss to explain how the disease is spread. 

In my investigations repeated trials failed to reveal the presence 
of either fungus or bacteria in culture. Nevertheless I do not believe 
with Woods that the disease is physiological and enzymie. I strongly 
believe, the trouble to be either bacterial or protozoic* and the patho- 
genic nature of the disease strongly points to this conclusion. That all 
attempts to obtain a living micro-organism in pure culture have failed 
does not argue against the possibility of its being either bacteria or 
protozoa, but simply that our present cultural or filtering methods 
are not suitable for its detection or retention. Previous to the discov- 
ery of Bacterium tumefaciens, by E. F. Smith, no one suspected the 
crown gall of plants to be of bacterial origin, cultural attempts in each 
case failed to reveal the organism. 

As I have already indicated, Beijerinck showed that the juice 
of diseased plants when filtered through Chamberland filters, while 
remaining clear and free from bacteria still retains the power of infec- 
tion. This proof too does not argue against the possibility of the bac- 
terial or protozoic nature of the mosaic, because the former may be 
even smaller than bacteria and readily pass through the Chamberland 
filters. It is therefore possible that Beijerinck 's filtered fluid was 
contaminated with the pathogen and this is why the filtered fluid 
retained its pathogenic nature. Neither can we accept Wood's state- 
ment that healthy plants when cut back develop the disease unless we 
admit again of the possibility of contamination. If the mosaic path- 
ogen is not present or has not made its appearance on a certain host, 
the latter can be cut back time and again without the disease ever 
making its appearance. Before I introduced the disease through punc- 
ture inoculation with diseased tissue in the laboratory, I cut back 
my experimental sweet pea plants in order to prevent them from 
growing too high and altho I have practiced this very often I have 
never had a case of mosaic develop from this operation. It is also 
difficult to believe with Woods that the disease is of a physiological 
and enzymie nature. Enzymes in plants are natural factors of im- 



*The idea of the protozoic nature of mosaic was suggested to me by Dr. T. 
F. Manns. 



60 

munity to protect that plant from disease. Diseased plants will nat- 
urally possess a higher enzymic content just as much as the leucocytes 
in the human blood increase in case of wounds, etc. That this per- 
oxidase of Woods from diseased plants should possess the power of 
infection is very possible as I have already pointed out the former 
may be contaminated. That the peroxidase of healthy plants when 
inoculated into a healthy plant should be able to produce the disease 
as Woods claims to have done, is probable, only if we admit of pos- 
sibilities of contaminations which may have been the case. As al- 
ready stated, the pathogenic nature of the disease points to a living 
organism as being the cause. 

In Wood's enzymic explanation we have no means of accounting 
for the spread of the disease. Under pathogenicity we have shown 
that green aphids carry and spread the disease from leaf to leaf and 
from plant to plant. This by itself is sufficient proof that a living 
organism is the cause of the mosaic, for if as Wood maintains, the 
peroxidase of a healthy plant when inoculated into a healthy host will 
reproduce the disease and if there be no chemical difference between 
peroxidase of healthy and diseased plants, then why is it when green 
aphids from perfectly healthy plants are transferred to healthy sweet 
peas the disease never develops but the mosaic readily makes its ap- 
pearance by introducing green aphids from diseased plants to healthy 
ones. If the aphids can carry the peroxidase from diseased plants why 
do they not carry the same from the healthy plants while sucking 
their juice? This to my mind is the strongest argument against 
Wood's physiological and enzymic nature of the mosaic, and on the 
other hand it strongly points to the probable activity of a living bac- 
terial or protozoic organism. Aphids are not the only agents capable 
of carrying and distributing the disease, for there are others which 
may do it. Among the biting insects we have the "corn root worm 
beetle" (Diabrotica longicornis), the striped potato beetle (Epicanta 
vittata) and several others which feed on the sweet pea and at the 
same time help to distribute the mosaic. 

Transmission of the Mosaic through Seed or Soil. Beijerinck 
claims that soil around diseased plants may infect the roots of healthy 
plants. In order to determine whether the disease is carried in the 
soil, the following experiments were tried. A number of sterile pots 
were taken and arranged in groups. Group A. consisted of pots filled 
with sterile soil, on the level surface of which leaves infected with 



61 

mosaic were spread. Sterilized seeds were sown on the surface of the 
leaves and the infected leaves and seeds were covered with a 2-inch 
layer of sterile soil. 

Group B. consisted of 2 pots filled with sterile soil but the latter 
was mixed thoroughly with a quantity of mosaic infected lieaves:. 

These pots were sown with sterilized seeds and covered with a 2-inch 
layer of sterile soil. 

Group C. consisted of two pots filled with sterile soil and sown 
with sterile seeds and then thoroughly watered with water from a vase 
in which mosaic infected plants stood for two days. 

Group D. consisted of two pots filled with soil taken from the 
field and from a spot where mosaic infected plants grew. 

Group E. were untreated checks, that is, two pots with sterile soil 
were sown with sterile seeds and placed at a distance from the infected 
series. All the pots were then watered with distilled water up to the 
end of the experiment. The seeds in all the groups germinated and the 
plants were allowed to grow for ten weeks when they had attained 
considerable size and in no case did the mosaic appear, thus appar- 
ently proving that 'the mosaic soil is not a factor in carrying the dis- 
ease. There is no evidence either that the mosaic is carried with the 
seeds for in no case did the disease appear in the laboratory where 
unsterilized seeds were used. 

Diseases of the Sweet Pea not known to be present in 

this Country 

In an article in "The Sweet Pea Annual," Massee 125 describes 
the following diseases, which as far as known, have not as yet made 
their appearance in this country on the sweet pea. 

Pea Blight (Peronospora trifoliorum) 

Pea Spot (Ascochyta pisi) 

PEA BLIGHT, Peronospora trifoliorum De By. 
According to Massee, this is the most destructive disease to 
peas, lupines, and to most of the pea family. The disease may 
appear and spread quickly when the plants are only a few inches 
high, or it may attack older plants. In dry weather the mycel- 
ium of 'the fungus present in the tissue spreads throughout the leaf, 



62 

which soon assumes a sickly yellow-green color, and finally bleaches, 
shrivels and dies without showing any, or only a small amount of 
mould on 'the surface. In damp, dull weather infected leaves show 
yellow patches, which soon becomes covered on one or both surfaces 
with a very delicate greyish-lilac mould. The summer spores, are pro- 
duced on the leaves, or on any other part of the host. The winter, or 
resting spores, are imbedded in the tissue of the host that has been 
previously killed by the fungus. The resting spores have a very thick 
smooth brown wall. Peronospora viciae is also stated to be able to 
produce a disease on sweet peas. 

PEA SPOT, Ascochyta pisi Lib. 

According to Massee, this disease also attacks the French beans 
and several other leguminous crops. The first indications of disease 
on the pods is the appearance of pale green spots of variable size and 
irregular shape. These blotches continue to increase in size for some 
time and eventually become whitish, bordered with a dark line, and 
have the surface studded with minute black points which are the 
pycnidia of the fungus. 

C. Diseased Seeds 

Under the discussion of the anthracnose disease I have shown 
that the fungus (Glomerella rufomaculans) is transmitted with the 
seed. In that case infection starts at the pods and the fungus works 
inwards gradually penetrating the seed coat and the seed proper 
(Fig. 38). Such seeds when harvested have a shirveled appearance 
and when planted with healthy seeds introduce the fungus in the soil 
and then the disease begins to attack the adjacent seedlings, thus 
spreading throughout the whole field. 

Another disease that may be transmitted with the seeds is the 
"Streak". In examining infected plants we can readily see the organ- 
ism (Bacillus lathyri) invade the pods and then work into the seeds. 
Pure cultures of the organism may readily be obtained by surface 
sterilizing an infected pod, picking out the seed with sterile forceps 
and then dropping the same into a plate of media. We have as yet 
no data to prove that the organism can survive the drying when it 
is only present on the surface of the seed coat. However, as is often 
the case, the organism works through the seed coat and into the seed. 
Under such conditions it is very probable that it may be carried over 



63 



winter while present in the seed tissue. Such seeds when planted 
introduce the parasite into the soil and from there the disease geto 
a foothold to carry on its destructive work. 

Sweet pea seeds as we buy them from the seedsmen are put in 
small paper packages. During my work on the sweet pea diseases 
I had occasion to open two thousand of such packages. In very few 




^3 

PI 

<0 



3 S 

pi 



&J0 



cases were all the seeds plump and full. A certain percent were shriv- 
eled and gave the appearance of being diseased. It was thought, 
therefore, advisable to make a study of such shriveled seeds to deter- 



64 



mine whether or not they are disease carriers and the nature of the 
pathogens. The technique employed was as follows: 

Fresh packages of sweet peas were opened and the percent, of 
shriveled seeds in each package determined, labeled and separated. 
The next step was to soak each lot of seed with a 5% formaldehyde 
solution for y 2 hr. and then to wash it three times in sterile water in 
order to remove all trace of formaldehyde. Then with a sterile for- 
cep, each lot of seeds thus treated was dropped into a petri dish con- 
taining nutrient agar that had been melted and cooled to the proper 
temperature. As the agar solidified the plates were placed in the incu- 
bator and kept there for one week. Observations were made every 
other day to determine the percent, of germination and to make trans- 
fers into slant tubes of agar of all fungus or bacterial growth which 
appeared on the shriveled seeds (Fig. 43). The results obtained are 
given in Table V from which will be seen that a large percentage of 

TABLE V 



Name of variety 
in package 



Per cent of shriv- 
eled seeds in 
package 



Per cent of germ- 
ination of shriv- 
eled seeds 



Kind of fungi obtained 
from non-germinated 
shriveled seeds 



King Edward VII 
Gray Friar 
Aurora 

Apple Blossom 
Emely Henderson 
Henry Eckfort 
Jeannie Gordon 
Dorothy Eckfort 
Hellen Pierce 
Coccineae 
Katherine Tracy 
George Herbert 
Black Knight 
Jeannett Scott 
Dobbies Mid Blue 
Blanche Burpee 
America 
Blanche' Perry 
Mrs. A. Watkins 
Countess Spencer 
Boltons Pink 
Countess Cadogan 
Agnes Eckfort 
E. J. Castle 
Mrs. Collier 
Burpees Midnight 



13% 


33% 


20% 


None 


X\J\J /c 

9% 


Botrytis cinerea 


12% 


6% 


None 


18% 


100% 


i t 


15% 


4% 


Fusarium sp. 


5% 


100% 


None 


13% 


80% 


Fusarium sp 


10% 


80% 


it 1 1 


6% 


90% 


e t cc 


15% 


■ 40% 


Alternaria 


19% 





Bacteria 


4% 


■ 100%. 


None 


21% 


10-0% 


it 


3% 


100% 


1 1 


12% 


100% 


a 


9% 


100% 


1 1 


1% 


100% 


1 1 


7% 


60% 


Fusarium sp. 


15% 


■ 18% 


Botrytis 


1% 




Clanostachys sp 


12% 


9% 


None 


16% 


■ 8% -■ 


Fusarium 


3% 


1% 


1 1 


10% 


50% 


1 1 








— 



65 

the so called shriveled seeds readily germinated. It was further ob- 
served that these before germination became plump and resembled in 
every respect the germinated healthy seeds which were treated in the 
same way as the shriveled and were run as checks. It seems then 
that shriveling in the seeds is merely correlated with a loss of water. 
Whether shriveled seeds in the long run produce weaker plants has 
not been determined. Observations so far have shown that the seed- 
lings from the germinated shriveled seeds were in every way equal 
in vigor to the seedlings of the germinated plump seeds. 

Of the non-germinated shriveled seeds, those which remained 
free from fungous growth can be classed as hard seeds and those prob- 
ably would have germinated if the seed coat had been pierced. The 
germinated seeds which showed growth of fungus or bacteria were at 
once seen to become soft and rotted. Of the organisms isolated from 
the non-germinated seeds there were two species of Fusaria, one species 
of Alternaria, one species of Clonostachys, Rhizopus nigricans and 
Botrytis cinerea. These after repeated trials failed to infect healthy 
sweet pea seedlings, thus seemingly proving that they are saprophytes 
and of secondary nature. Their presence on some of the weak and 
non-germinated seeds, no doubt helped in the decay of the former, but 
they fail to play the role of active parasites on growing plants. 

II. Bacterial Diseases 

So far only one kind of bacterial disease of the sweet pea has 
been observed and that is the "streak" disease. This has been deter- 
mined to be caused by a newly described organism, viz. Bacillus lathyri 
Manns and Taubenhaus. 

STEEAK IN ENGLAND 

Historical. In correspondence with Mr. T. A. Weston of Or- 
pington, England, the former states that the disease was first observed 
by H. J. Digges of Dublin in about 1904 or 1905. 

In 1906 T. A. Weston 126 gave the name of "streak" to the dis- 
ease referred to above (the cause of the disease was not given). In 
1908 Massee 127 in a letter to a correspondent who had sent in diseased 
specimens replied, "the disease is of a physiological nature" and 
"brought about by over feeding." In 1912 Chittenden 128 believed 
that the fungus Thielavia basicola was the cause of the "streak". 
For the first two years of his inoculation experiments Chittenden 



66 

failed to infect healthy seedlings with the Thielavia fungus. It was 
only by overwatering his plants that he succeeded in getting some root 
infection, as he states : " To sum up, as far as our experiments go, the 
- streak ' disease is brought about by the attack of the fungus Thielavia 
basicola on plants that have received some check at the root." Chit- 
tenden has failed to reproduce the typical "streak" but merely the 
Thielavia root rot as I have already indicated under my description 
of the above fungus. In the same year Massee 129 again studied the 
disease and attributed it to Thielavia basicola. 

In 1912 Dyke 130 found Macrosporium solani constantly associa- 
ted with the disease, and believed it to be the cause of the trouble. 

STEEAK IN THE UNITED STATES 

As far as I know, up to 1913 there were no American references 
to this disease. 

Massee's 131 short note led me to believe that the disease was phy- 
siological. Under Mosaic disease, I have shown that some workers be- 
lieved it to be a physiological disease. While working on the mosaic, 
and having the "streak" in mind, I 132 made the following statement: 

"In England the sweet peas suffer from a disease known as 
'streak'. This disease is very much dreaded by English gardeners, 
as it causes great losses. From the description given of that disease 
it seems to be similar to the new mosaic disease of this country. How- 
ever, we refrain from passing final judgement until we have the op- 
portunity of seeing the English specimens and of making compari- 
sons. In England the streak disease is attributed to a fungus Thiel- 
avia basicola, which attacks the roots. In our investigations we have 
not found the Thielavia fungus or any other organism associated on 
the roots of mosaic affected plants. In fact, such affected plants were 
found to have as normal a root with as much in the way of legume 
nodules, as the healthy ones. If our mosaic disease proves to be the 
same as the streak disease of England, it will be safe to assume that 
the Thielavia in England is secondary and merely follows the already 
weakened mosaic affected plant." 

The above was published on July 20, 1912, and the statement 
was made before the American Sweet Pea Society at Boston early in 
July of the same year. 

In the middle of July of 1912, I first noticed a peculiar disease on 
the stems of sweet peas grown in our experimental field. The disease 



67 

was characterized by dark streaks running along the stems. This sug- 
gested at once the possibility of its being the "Streak" disease of Eng- 
land. Diseased specimens were brought in the laboratory, and micro- 
scopical crush mounts were made, but no organism was found that 
would give any clue as to the nature of the trouble. 

In submitting specimens to Prof. Manns and in consultation with 
him, it was suspected that the trouble might be of bacterial origin. 
We at once started 'to make cultures from the diseased material and a 
pure culture of a yellow bacterium was obtained. Platings made from 
diseased material from widely separated gardens gave a pure culture 
of the same bacterial organism. Cultures made from diseased mate- 
rial sent in by Wm. Sims of Boston, Mass. and by T. A. Weston of 
Orpington, England, all gave an organism similar to that isolated 
from the home material. Stains made of this organism revealed a 
bacillus sp. In 'the meantime Prof. Manns recalled that he had seen 
a similar streak disease on clovers in Ohio. A search for plants in- 
fected in this way showed it upon clovers and upon some other 
leguminous plants in the vicinity of Newark, Del. 

Inoculations made with the bacterial organism on 'the sweet pea 
reproduced the typical "streak" disease. That the "streak" is pre- 
sent and widespread in the United States there is no doubt. I have 
seen it in widely different localities in Delaware, in Pennsylvania, in 
Massachusetts, and in New York. A letter addressed to me by C. C. 
Morse & Co., of California, gives the folowing information: 

"The 'streak' disease has not appeared in California as yet, and 
this is accounted for by the fact that growers so far have not gotten 
into methods of over-manuring their grounds." 

As previously stated, the American literature contains no refer- 
ence to the disease. Manns and Taubenhaus* published their first 
account of the disease in the Gardeners' Chronicle of England, an- 
nouncing the "streak" as being a bacterial disease and the parasite a 
newly described bacillus, giving it the name of Bacillus lathyri. 

" Symptoms A Like the Bacteriosis of beans, streak makes its 
appearance in the season of heavy dew. On the sweet pea the disease 
usually appears just as the plants begin to blossom ; it is manifested by 



*Manns, T. F., and Taubenhaus, J. J. "Streak, a Bacterial Disease of the 
Sweet Pea and Clovers." The Gard. Chron., London, Apr. 5, 1913. 
t Abstracted from above article. 



68 

light reddish-brown to dark brown spots and streaks (the older almost 
pnrple) along the stems, having their origin usually near 'the ground, 
indicating distribution by spattering rain and infection through the 
stomata. The disease becomes quickly distributed over the more ma- 
ture stems until the cambium and deeper tissues are destroyed in con- 
tinuous areas, when the plant prematurely dies. From the stems the 
disease spreads to the petiole, flower, peduncles and pods. The symp- 
toms in these cases being similar to those on the stems. On the leaves, 
however, the disease appears as small roundish spots which gradually 
coalesce, and eventually involve the entire leaf, which when killed 
presents a brownish dark appearance." 

Pathogenicity. The pathogenicity of the causative organism 
may be proven by diluting a pure culture of the organism in sterilized 
water and by spraying on the plants with an atomizer. This should 
be done in the evening when the temperature is cooler and there is 
less chance for evaporation of the applied infectious liquid. 

The disease makes its appearance from seven to ten days after 
artificial infection and the symptoms are similar to those produced 
in nature. The organism may be reisolated from the artificially in- 
fected plants and the disease induced again at will on healthy plants, 
in each case the check remaining healthy. 

Natural or artificial infection can only take place on mature 
plants which have started to bloom. All attempts to inoculate plants 
in all stages of growth previous to the blooming has failed. It seems 
that the host possesses certain protective properties previous to the 
blossoming which inhibits the growth of the parasite. Failure to in- 
fect young plants was not due to abnormal conditions or to bad tech- 
nique. The disease in the field does not make its appearance until the 
plants have started to blossom. 

Isolation and Morphological Studies. Over 1,500 plate cul- 
tures of beginning or young lesions were made from the several hosts. 
The organisms may almost invariably be taken in abundance in pure 
cultures from the beginning lesions in the stems of sweet peas when 
the surface is properly sterilized. 

The isolation work readily indicated the parasite to be a bacter- 
ium ; a yellow organism which grows luxuriantly upon all the nutrient 
media, and especially rapid upon nutrient media containing sugars. 



69 

On standard nutrient glucose agar the colonies appear within 24 to 36 
hours. The center becomes granular and the colonies have a marked 
tendency to become stellate or auricula'te. 

Morphological studies show the organisms to be a comparatively 
small rod-shaped bacillus, which in fresh cultures is rarely found in 
chains, and seldom united in twos or fours. The flagella are not easily 
demonstrated; they are shed so readily that usually not more than 
two to five may be stained, and these are generally quite short. How- 
ever, when proper material is selected, carefully fixed and stained, 
the flagella may be demonstrated 'to be very long and delicate, and to 
number 8 to 12, well distributed peritrichially*. 

III. Physiological Diseases 

By physiological diseases of the sweet pea we mean all disturb- 
ances in the plants which are not induced by fungi, bacteria, in- 
sects, or any other parasites but is expressed in a disturbance in the 
metabolism of the plant. This disturbance seldom results in the sud- 
den death of the plant. 

Under Physiological diseases I will consider the following two 
troubles: 1. Bud drop. 2. Arrested development. 

BUD DROP 

As the name implies the young flower buds at a very early 
age turn yellow and drop off. This drop should not be con- 
fused with the drop produced by the anthracnose disease. In the 
latter case, the flower develops into a normal spike but it is attacked 
soon by the fungus Glomerella rufomaculans which girdles it at a 
point of attachment between the flower and the peduncle. In this case 
the flower often drops off leaving behind the beheaded peduncle. In 
the latter case, however, the minute young flower bud never developSj 
instead it turns yellow and drops off. 

There seems no doubt that the drop is a physiological disease and:' 
is induced by an unbalanced condition of food elements in the soil. 
This may occur in a soil that has been excessively fed or in a soil that 
is lacking in plant food. 

The following extract of a letter from a grower whose plants have 
suffered severely from the drop and who gives the history of his soil 



*A more detailed account of this organism will soon appear in a Delaware 
Bulletin by Dr. T. F. Manns. 



70 

treatment will help to confirm the physiological nature of the disease. 

' ' The soil is rich and is located in a valley near a creek, the sub- 
soil is similarly rich but is not of a mucky nature. Before sowing the 
peas the field was trenched and a thick layer of pig manure mixed 
with a little hen manure was put at the bottom of the trench. The 
manure was mixed up with soil in the trench and the seeds sown 
thereon. After germination and when the plants reached from 8 to 10 
inches, a commercial fertilizer (kind of fertilizer not stated) was 
worked in at both sides of the row. A short time before blooming, a 
layer of coarse stable manure was put around the plants to serve as 
a mulch. During blossoming time the flower buds began to drop off 
heavily and what promised to be a successful crop of blooms looked as 
though it would result in total failure." It is here very evident that 
the plants were supplied with too much nitrogenous matter but with 
little of potash and other mineral elements. 

Cultures made from these fallen buds failed to produce an organ- 
ism of any kind. 

In order to remedy this trouble Prof. T. F. Manns suggested the 
application of 150 lbs. muriate of potash and 600 lbs. acid phosphate 
per acre. This treatment was followed out by the grower and the 
drop ceased within a week resulting in a perfect crop of flowers. 

On poor soils I have often seen this same "flower drop" and it 
is also especially evident where sweet peas are grown in pots and in 
poor, light, gravelly soil in the laboratory. An application of a bal- 
anced fertilizer to these pots readily helped the plant to overcome 
the bud drop. 

ARRESTED DEVELOPMENT 

This trouble, too, is a physiological disease and is induced by the 
use of excessive fertilizers. The following facts from the letter of 
a grower who has suffered from this trouble will also help to confirm 
the belief in the physiological nature of the disease. 

The seeds were sown Nov. 1st in pots and planted Dec. 15 in 
the beds in the greenhouse. Previous to the planting the beds were 
well manured with horse manure which was applied six months before 
planting. Besides this, wood ashes were also applied to the beds at 
the rate of 1500 lbs. to 4500 sq. feet of bed space. This would be 
equivalent to nearly seven and one-half tons per acre. About one 



71 

month after planting some of the plants turned yellow and died. 
Upon examining the dead diseased specimens the plants were found 
to be dwarfed with a sickly yellowish appearance. The roots pre- 
sented a burned appearance suggesting the attacks of Thielavia. 
Microscopical examinations and cultures made from the diseased tis- 
sue did not reveal the presence of any parasite which could be asso- 
ciated with the soil. In submitting some of the soil to Prof. T. F. 
Manns for examination, he found it strongly alkaline. Hard wood 
ashes contain about 30% caustic lime and from 5 to 12% potash. Ac- 
cording to Prof. Manns it was the excess of these elements in the soil 
that made it so highly alkaline, and this condition injuriously affect- 
ed the plants. This kind of injury could be considered purely phy- 
sical since it is brought about by the exposed surface of the roots to 
an alkaline substance. Nevertheless any injury which interferes with 
the metabolism of the roots is reflected in a derangement of the meta- 
bolism of the plant. The resulting injury is therefore of a physical 
nature. 

As a remedy for this trouble Prof. Manns advises the use of acid 
phosphate, followed by a good drenching of water. This will neu- 
tralize the alkaline effect of the soil and also help to balance the plant 
ration. 

METHODS OF CONTROL 

Under methods of control the following lines of investigation 
have been carried on : 
Resistant varieties 
Seed treatment 

Treatment of soil with chemicals 

Studies of the fungicidal value of some chemical poisons 
Formaldehyde treatment of soil 
Steam treatment of soil 

RESISTANT VARIETIES 

To test out the resistance of different varieties of the same host 
to a certain parasite, the general practice is to plant in the field the 
varieties to be tested and to allow full sway to the natural causes of 



72 

infection. At the end of the growing season an estimate is taken of 
the per cent of infection of each variety and on that basis a scale of re- 
sistance is formulated. While this method by itself is fairly val- 
uable, the method nevertheless is unreliable because a certain va- 
riety which under the above test proves highly immune or highly sus- 
ceptible to disease will, under different conditions of climate, etc. prove 
the opposite of what it has promised to be in its first trial. The reason 
is very obvious. No two varieties are alike as well as no two individu- 
als are alike. Conditions in the field are not always ideal for every 
variety of a certain host to become susceptible to disease. If this were 
the case we would have all our crops ravaged by pests. In order to 
make a reliable test of the resistance of different varieties it is 
necessary to have the same conditions of soil and care and then to 
submit the varieties to the severest test by making all conditions ideal 
for the parasite to attack the plants. To carry out this idea, I planted 
100 sweet pea seeds of each variety to be tested in sterile soil and pots 
in the laboratory. Previous to the planting, the seeds were sterilized 
by being soaked in a 5% formaldehyde for i/ 2 hr. The seeds 
of the different varieties did not all germinate evenly due to 
the hardness of the seed coats in some seeds but eventually they 
all germinated. When the plants were eight weeks old ■ each pot 
with its different variety was well watered and then covered with 
a bell jar. The latter was sterilized by being previously washed 
with a 1-1000 mercuric bi-chloride solution and then rinsed with 
distilled water. The plants remained under the bell jars for 48 
hours, where all were seen to be uniformly covered with drops 
of water. A large amount of moisture accumulated under the bell 
jars and this was plainly visible by the drops of water standing on 
their walls. Under such conditions of moisture as described above, 
infection readily takes place. The infecting material chosen for this 
purpose was the fungus G-lomerella rufomaculans, which causes the 
anthracnose disease. Accordingly a heavy suspension of spores from 
a pure culture was diluted in sterilized water and then applied to the 
plants by means of an atomizer. The inoculated plants were covered 
again for 48 hours. After that the bell jars were removed and the 
plants left uncovered. The result of the experiment is given in 
Table VI. 

From Table VI it is seen that of all of the varieties tested not one 
of them proved to be entirely resistant. On the other hand it is seen 



73 



that the percent of infection differs with the variety. This means 
then that in each variety there are certain individual plants which 
are resistant to this particular fungus tested. Attempts were made 
to reinfect those plants which remained healthy after the first inocu- 
lation and it was found that nearly 50% in each case was infected 
and the rest remained resistant and continued to grow well. This con- 
clusively shows that while no one variety is entirely immune to a dis- 
ease yet there are nevertheless certain individuals of that variety 
which have developed the power of resistance. It is well known that 
if a plant is resistant to a particular disease, it may be very susceptible 
to another disease. The problem, therefore, is to test the desired va- 

TABLE VI 



Name of variety (seed- 
lings six weeks old) 

King Edward VII 
Gray Friar 
Aurora 

Apple Blossom 
Emery Henderson 
Henry Eckfort 
Jeannie Gordon 
Dorothy Eckfort 
Hellen Pierce 
Coccineae 
Katherine Tracy 
George Herbert 
Black Knight 
Jeanett Scott 
Dobbie Mid Blue 
Blanche Burpee 
America 
Blanche Ferry 
Mrs. A. Watkins 
Countess Spencer 
Black Michael 
Bolton 's pink 
Countess Cadogan 
Mrs. Bieberstedt 
Agnes Eckfort 
Burpees Dainty 
E. J. Castle 
Glady 's Union 
Captain of the Blues 
Duke of Westminster 
Mrs. Collier 
Burpees Midnight 




100% 

92% 

70% 

70% 

60% 

80% 

72% 

40% 

90% 

100% 

100% 

100% 

90% 

60% 



100% 

20% 

100% 

100% 

1% 

4% 

60% 

80% 

70% 

40% 



rieties with all the known diseases to which they are subject. In these 
•tests all the immune individuals must be selected and by crossing and 



74 

selecting we will build up a strain which will possess complete immun- 
ity to all or at least to most of 'the diseases to which that variety is 
subject. 

SEED TREATMENT 

I have previously shown that the sweet pea seeds are capable of 
carrying and of introducing one of the most dreaded diseases of the 
sweet pea, namely, the anthracnose (G-lomerella rufomaculans) . 
Sweet pea seeds were also found to carry several species of fungi 
which seem to be unable to assume the role of parasites. Nevertheless, 
the time may come when these fungi may become parasites of the 
sweet pea. 

It was, therefore, thought necessary to devise some means of 
treating the seeds which woud kill all external as well as internal 
parasites, and at the same time not inhibit the germinative power of 
the same. The following are the methods which have been tried : 

Effect of temperature 

Effect of sulphuric acid treatment 

Effect of formaldehyde treatment 

Effect of Temperature on Seed. In order to test the effect 
of temperature the following experiments were tried. Ten differ- 
ent varieties were thoroughly mixed and lots of 100 seeds each were 
picked out and put in pieces of cheese cloth and tied up with a string. 
The experimental temperatures of the water used were boiling water, 
90°, 80°, and 60° C. The seeds were immersed in the water with the 
varying temperatures and kept there for different intervals of time, 
as is indicated in Table VII. In each test a duplicate series was al- 
ways made, i. e. using two packages of 100 seeds each. The per cent 
of germination in each case expresses 'the average taken from each 
duplicate series. After each treatment seeds were placed in sterilized 
petri dishes containing moistened filter paper which had been pre- 
viously sterilized by being placed in boiling water for two minutes. 

After placing the seeds in the petri dish more sterile water was 
added in order to secure the amount of moisture necessary for ger- 
mination. The plates were then placed in the incubators for 10 days, 
observations being made every two days. The result of the experi- 
ment is given in Table VII. 



> 

J 

CQ 
< 


spaqD 

o 
O 


: 


ao 


b« 


^. 


h J= 




k— Killed *Note— This treatment would not be successful where several pounds of seed are treated at a time, 
g— Good as the boiling temperature would not reach the center in the time allotted, 
w — Weak 


p — Peniceliium 

r-"-Rhizopus 

b — Bacteria 

s — Sterigmatocystis 




ntw OC 


ON 


is 


~ 


P..O « u 


no 




ujk ST 


^0 


£ 


44 


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76 

From Table VII it is seen that of all the temperatures tried, 
placing the seeds in boiling water for one or two seconds, seems to 
offer only little promise of success. 

Placing the seeds in water of 90° C. for one minute insures a 
somewhat higher per cent of germination. However, the growth of 
seedlings seems to be weaker than either checks or those boiled for 
one or two seconds. 

The series treated with water at temperatures of 80° C, 70° C, 
and 60° C. did not meet our expectations of success. However, these 
results are not final, as they simply open up a line of investigation 
for the future. 

Effect of the Sulphuric Acid Treatment on Seed. Historical. 
Rostrup 133 was one of the first investigators to use sulphuric acid 
on hard seed in order to hasten germination. Todaro 134 , while 
working independently, found that concentrated sulphuric acid 
of a density of 1.84 acted upon hard seeds of many leguminous plants, 
rendering them capable of prompt germination. Thornber 135 , too, 
found that when certain seeds are treated with sulphuric acid, tbeir 
germination was hastened. Schneider-Orelli 136 also found the sul- 
phuric acid treatment of value in hastening the germination. Bol1ey 137 
also found sulphuric acid to benefit the germination of seeds. In 1912 
Love and Leighty 138 also found the same general beneficial results on 
germination of seeds treated with sulphuric acid. 

My object in treating sweet pea seeds with sulphuric acid was to 
find out its effect on germination, and as a preventive means in de- 
stroying all possible adhering spores of pathogenic organisms. The 
method was to place the seeds to be treated in glass receptacles and 
then to cover the seeds with pure sulphuric acid. The time of treat- 
ment was five minutes, fifteen minutes, one-half hour, one hour and one 
and a half hours. After the treatment the acid was poured off and 
the glass receptacle was put under running tap water for five min- 
utes and then rinsed three times in sterilized water. After that the 
seeds were placed on moist filter paper in petri dishes, and the latter 
were put in the incubator for ten days. A series of untreated seeds 
were also run as checks. 

The results obtained from the seeds treated five minutes, fifteen 
minutes and one-half hour were practically the same, i. e., in each 
case the percentage of germination was much higher in the treated 



77 

seeds 'than in the checks. In the former the percentage of germination 
ranged from 95% to 100%, while in the later it ranged from 
60% to 85%. The seeds treated in the acid for one hour showed 
50% injury, and the iy 2 hour treatment gave only 2% germination. 
In order 'to test the effect of sulphuric acid on the fungus flora 
of the seeds, 10 cc of the acid was put in test tubes, and the latter 
were inoculated heavily with spores of Grlomerella rufomaculans and 
allowed to stand for five minutes, fifteen minutes, half-hour and one 
hour. Transfers of the treated spores were made by means of a loop 
into melted tubes of agar. These were well shaken and poured into 
petri dishes, cooled, and placed in an incubator. Check cultures were 
also run by using untreated spores transferred directly into agar. In 
three days the check plates all showed a vigorous growth of a pure 
culture of the fungus where none of the series of the treated spores 
showed signs of germination even after eight days. This proves, then, 
that sulphuric acid can be used with advantage in treating seed both 
to increase the per cent of germination and also 'to kill all spores 
which adheres to the seed coat. 

Formaldehyde Treatment of Seed. The method employed here 
was the same as for the sulphuric acid. The strength used was 5%, 
and the time of treatment was five minutes, fifteen minutes, half hour, 
one hour and one and a half hours. It was found that the one and a 
half hour treatment seemed to have reduced the percentage of germin- 
ation, whereas, all the other treatments did not affect in any way the 
germination. 

"Where there was no injury apparent, the formaldehyde treatment 
did not seem to help the germination of the seeds as did the sulphuric 
acid. However, it no doubt helps to kill the adhering fungus spores 
of the seed coat. This latter advantage makes the formaldehyde 
treatment a valuable preventive means. 

TREATMENT OF SOILS "WITH CHEMICALS 

The object of this treatment was to determine : 1, the effect of the 
treatment on the growth of the plant and its resistance to disease; 
2, the effect on the soil flora ; and 3, the effect on the nitrogen content 
and ammonification. The method employed was to sow 50 seeds in a 
pot (18 pots in all) ; the soil employed was unsterilized light garden 
learn. 



78 



The chemicals and 'the strengths used are indicated in Table VIII. 
After the seed had germinated and the plant had attained three inches 
in height, I began to water them twice a week with the respective 
chemicals. The checks were treated with distilled water. The experi- 
ment was run for two seasons, in each case up to the flowering time 
of the host. 

The results of the first season are not indicated in Table VIII 
because with one exception as stated below there was no apparent dif- 
ference between the treated and the check plants. During the first 
season, the treatment did not affect in any way the fungus or bac- 
terial flora of the soil. Both treated and check plants, before the 
close of the first season, were inoculated with spores of Glomerella 
rufomaculans. But both lots gave about 'the same percentage of in- 
fection. This clearly indicated the wonderful power of the soil to 
absorb mineral poisons and to fix them in such a way as to make them 
harmless 'to plant growth. Ordinarily, neither plant, fungi, nor bac- 
teria could grow in a solution of 1-1000 copper sulphate, for instance. 
However, when this same solution is applied to the growing plants 
through the soil, the latter fixes it so that the plants continue their 
growth and reach maturity as they would if the copper sulfate were 
not there. The same holds true for the soil flora. 

The only injury apparent to the plants during the first sea- 
son's trial was on the series watered with 1/100 MnS0 4 . Altho grow- 
ing fairly well, these plants were seen to lose their chlorophyll at an 
early date. These plants died just before blossoming, and at that 
stage they were white with no trace of chlorophyll. 

The results obtained from the second season's growth are tab- 
ulated in Table VIII. 

In order to determine the effect of the different chemical treat- 
ments on the soil flora, the method employed for isolating the organ- 
isms was the same as that recommended by Prof. T. F. Manns 139 . 
Plates containing 1/1000 and 1/10,000 of a gram of soil was made. 
Two kinds of media were used for this purpose, the composition of 
which is given in Table VIII. The media marked XXI is purely syn- 
thetic and is of value in bringing out the azotofiers. It is also valuable 
in bringing out the bacterial flora of a soil and in keeping down 
the saprophytic fungi. Medium II on the other hand, is more likely 
to bring out the fungus growths and to keep in check the bacterial 





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79 

flora. The nitrogen was determined* according to the Kjeldahl 
(modified) method 140 . 

Ammonification was determined by inoculating 100 cc of nutrient 
broth containing one gram of peptone with 1 cc of an infusion made 
by shaking 10 grams of soil in 100 cc of water. 

From Table VIII we see that the results obtained vary consid- 
erably, especially during the first six days, which more nearly rep- 
resents the ammonifying power. Under copper sulphate for instance, 
1/1000 killed 70% of the seedlings and the growth of the latter was 
quite stunted. The average number of bacteria per gram of soil was 
also less when compared to the checks, whereas there was an actual in- 
crease in the nitrifiers, which resulted in an increase of total nitrogen 
and ammonia. On the other hand, copper sulphate 1/3000 produced 
stimulation in plant growth; there did not seem to be an appreciable 
decrease in the general bacterial flora, but there was a resultant de- 
crease of ammonifiers. Again, under Hg Cl 2 1/2000, the result was 
a killing of all the seedlings, but an increase in the bacterial flora as 
well as nitrification and ammonification. Hg Cl 2 1/4000 gave stimula- 
tion in plant growth, soil flora, and in ammonification. 

Table VIII is extremely interesting, as it opens up so many new 
phases in soil biology, soil bacteriology, and in plant pathology. 

STUDIES OF THE FUNGICIDAL VALUE OF SOME 
CHEMICAL POISONS 

Those who are actively engaged in the study of methods of con- 
trol in plant disease, will readily realize how uncertain it is to depend 
upon field methods alone. In order to test out the value of a fungi- 
cide the only method used consisted in spraying the particular plant 
to be treated, with that fungicide, and of noting results. With such 
a method one works in the dark. Moreover, a great deal of time is lost, 
because each trial, or each modification of a trial means one season 
of growth. In 1910 Reddick and Wallace 141 worked out a quick 
method of determining the efficiency of a certain spray material. In 
brief, the method is as follows : 

The fungicide to be tested is sprayed on a clean slide with an 
atomizer. It is then allowed to dry in order to permit any chemical 



*Mr. Paul Emerson under the direction of Prof. Manns carried out this 
phase of the work. 



80 

changes to occur that are likely to be induced by exposure to atmos- 
pheric conditions. It is supposed that the same chemical changes 
which take place on the leaf previous to infection also take place on 
the slide in the laboratory before the spores are placed to germinate. 
This more nearly duplicates natural conditions, and the results at 
time of germination practicaly indicate the relative fungicidal value 
of the chemical tested. When thoroughly dry, each slide is placed in 
a petri dish containing enough water to keep the air well saturated. 
Spores of the particular fungus .which we wish to control are mixed 
in water, and drops of this water are placed, with a dropper, on the 
treated slide. The pe'tri dish is now covered and 24 hours are allowed 
for the spores to germinate. The inhibition of germination of all the 
spores in the drops placed on the slide indicates the value of the fungi- 
cide. While the method above described is excellent, it nevertheless 
has its drawbacks. We know that in practice we do not spray our 
plants every day, but this is usually done every three or four weeks. 
The method employed by Reddick and Wallace cannot account for 
the fungicidal value of a certain spray material during the two or 
three weeks from the time of its first application. In my studies I have 
supplemented this deficiency 'by the following method. While adopting 
the method used by Reddick and Wallace of applying the fungicide 
and of drying the slide, I have worked out the following modifications. 
Instead of spraying only a few slides and of inoculating them at once, 
I have sprayed some fifty slides at one time with each chemical. 
These slides were all dried and divided into different lots. Lot I was 
used for germination at once, lo't 2 used, say, after an interval of one 
week, etc. This method allows the time element to have its full effect 
on the fungicide concerned, and each germination test definitely indi- 
cated whether that fungicide deteriorates rapidly or not. The fungi- 
cide which preserves its germicidal value the longest is probably of 
the greater economical value. The fungicides tested and the strengths 
used are indicated in Table IX. 

It will be seen from the above table, that copper sulfate at the 
strength of 1/100 up to 1/500, and potassium permanganate y 2 % up 
to 3% completely inhibited the germination of the spores of G-lom- 
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sulphur 1/10 up to 1/50 gave most unsatisfactory results from the 
very first test, and its fungicidal value rapidly weakened with age. 
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82 

known as ' ' Liver of Sulphur. ' ' Lime sulphur is a valuable fungicide 
in controlling apple scab (Venturia inequalis) and sulphurated 
potassium is a valuable fungicide in controlling mildew (Oidium sp.), 
but evidently these two fungicides are of no value in the control of 
the sweet pea anthracnose. On the other hand, copper sulphate and 
potassium permanganate both prove very toxic to the spores of the 
anthracnose. The next step therefore, was to test all the strengths 
used of these two fungicides by spraying them on sweet pea plants in 
field, and by watching to see if these poisons produced burning of the 
leaves and stems. Copper sulphate at the strengths of 1/100, 1/200, 
1/300, 1/400 and 1/500 all burned the leaves of the sweet pea. Hence 
while the above strengths possess valuable germicidal properties their 
use upon the sweet pea is prohibitive. This means that weaker 
strengths are to be tried until 'the proper limit is reached, i. e. the 
limit which does not decrease the germicidal value of the copper sul- 
fate and which does not produce injury to the plant. This we intend 
to carry on further in the future. Potassium permanganate %% up 
to 3% does not produce any injury to 'the plant whatsoever. As a 
matter of economy, therefore, y^% of potassium permanganate proves 
a valuable fungicide in the control of the sweet pea anthracnose. It 
should be applied to the plant not oftener than it is washed off by 
rain. The method can be used in testing out an endless number of 
chemicals and there is no doubt that a good many will prove valuable 
additions to our list of fungicides. 

Soil Treatment in the Greenhouse 
Growers who are troubled with Khizoctonia or Fusarium in their 
greenhouse beds, will find the following directions valuable 142 . 

STEAM STEEILIZATION 

"The preventive method which promises best results to those who 
have the convenience for applying it is that of sterilization of the seed 
beds by steam. 

"In addition to the killing of the fungus, this method, in com- 
mon with surface firing, to be described later, has several advantages 
over formalin treatments. The weed seeds in* the soil are very largely 
killed, and this alone, according to the testimony of the farmers who 
have used sterilization, pays for the cost of treatment, as the beds do 
not have to be weeded and thus a large amount of hand labor is ob- 
viated. The physical texture of the soil is altered by the heat and 



83 

made more suitable to root development and, moreover considerable 
plant food is made directly available to the seedlings. Furthermore, 
the heating of the soil just before sowing in the spring has an ap- 
preciable effect in starting the seedlings off quickly. 

"With the elimination of the fungus it is possible to employ 
those methods forcing the plants by extra fertilization, increased 
watering, and higher temperature which would otherwise be unsafe 
as favoring the development of 'the root-rot fungus. 

" Ordinary greenhouse method — The method of sterilization to 
be used will depend to some extent on the size, the location, and "the 
permanency of beds and the cost of application. 

' ' The method in general use for the sterilization of soil in green- 
house benches might advantageously be employed in beds that are 
to be used year after year without change of location, as the equip- 
ment would be more or less permanent. This consists in placing one 
foot below the surface of the soil a system of 1%-inch pipes which 
are perforated with 14-inch holes on their under side at intervals of 
6 inches throughout their entire length. The pipes should run 
lengthwise of the bed, 18 inches apart, and be connected with a steam 
boiler capable of producing 80 to 100 pounds pressure. Before treat- 
ment 'the soil should be thoroughly spaded up and pulverized to permit 
ready access of the steam to all parts, and all fertilizers should be 
applied at this time. 

' ' The bed to be treated should be covered with several thicknesses 
of old burlap or blankets to confine the heat to the soil. The steam 
should be applied at a pressure of 80 to 100 pounds, as at a high 
pressure it is much drier and the soil is not wet as much as when low- 
pressure steam is used. A treatment of from one to two hours is 
usually sufficient to thoroughly sterilize the soil to a depth of 18 inches. 
A few potatoes laid in the surface will indicate the thoroughness of 
the treatment by the degree to which they are cooked. The blankets 
might advantageously be left on for some 'time to make the treatment 
more thorough. 

"While this method offers some advantages for seed beds of lim- 
ited area, in that the pipes may be left in the ground and used year 
after year with little extra labor and may also be used for subirriga- 
tion, the initial cost of installation, especially on large seed-bed areas, 
may be prohibitive. 



84 

" Inverted-pan method. The method which has given the best re- 
sults in practice, and which because of its simplicity and small cost 
recommends itself for use on large or small areas, is the invention of 
Mr. A. D. Shamel, of the Bureau of Plant Industry, and was devised 
by him to sterilize nematode-infested soils in Florida. The apparatus 
consists of a galvanized iron pan, 6 by 10 feet and 6 inches deep, which 
is inverted over the soil to be sterilized and the steam admitted under 
pressure. The pan is supplied with steam hose connections, has 
sharp edges, which are forced into the soil on all sides to prevent the 
escape of steam, and is fitted with handles for moving it from place to 
place, the weight of the entire pan being not over 400 pounds. 

' ' The soil is prepared as in the greenhouse method, a few potatoes 
being buried at a depth of a foot to gauge the degree of heat attained. 
A soil thermometer may also be used if desired. The steam should be 
kept at as high a pressure as possible, 80 to 100 pounds being best, 
and the treatment should continue for one to two hours, depending on 
the pressure maintained. In experiments conducted in the spring of 
1907, one hour's steaming at 80° C. under 100 pounds pressure gave 
best results in killing both the fungus and the weed seeds. When one 
section of the bed is treated the pan is lifted and carried to an un- 
sterilized portion and the operation repeated until the entire bed is 
steamed. 

FOBMALDEHYDE STEBILIZATION 

"The use of a formalin solution for the sterilization of green- 
house soil against Rhizoctonia has been in vogue for some time with 
excellent results, and furnishes a very simple means of combating the 
root-rot. The method is as follows: The beds are thoroughly pre- 
pared the same way as for the other methods of sterilization described 
and are then drenched with a formalin solution composed of 1 part 
of commercial formalin to 150 to 200 parts of water, three-fourths 
to 1 gallon of this solution being used to the square foot of bed space. 
The solution should be put on with a watering pot with a hose and 
distributed as evenly as possible over the bed, so as to thoroughly wet 
the soil to the depth of a foot. It will in most cases be necessary to 
put this solution on in two or three applications, as the soil will not 
take in this quantity of water immediately. The beds should then be 
covered with heavy burlap or a tarpaulin to keep in the fumes for a 
day or so, and then aired for a week before sowing the seed. 



85 

''Spring applications of formalin are open to the following ob- 
jections: The addition of such a large quantity of water to the soil 
keeps it wet and cold for some time longer than would naturally be 
the case, thus delaying germination as well as subsequent growth ; the 
necessity of airing the beds to remove the formalin fumes and to allow 
the soil to dry out also causes delay in seeding. To obviate this dif- 
ficulty the beds should be treated in the fall, before freezing weather 
sets in. In this case a stronger solution, 1 to 100, may well be used, 
as there will of course be no danger then of injuring the seedlings." 

SUMMAEY 

1. It has been shown that the sweet pea is subject to a number of 
diseases. 

2. The following classes of diseases have been investigated: 
I. Fungous; II. Bacterial; III. Physiological; IV. Animal or In- 
sect Pests. 

3. Contrary to the statements of Massee and Chittenden, Thiel- 
avia basicola does not produce the ' ' streak, ' ' but produces only a root 
rot of the sweet pea. 

4. The pathogenic nature of Corticium vagum B. & C. has been 
established. 

5. Chaetomium spirochaete has been shown for the first time to 
be a plant pathogen, and especially to produce a root rot of the sweet 
pea. 

6. A new Fusarium root disease has been described, and the name 
Fusarium lathyri Taubenhaus has been given to the fungus, and its 
pathogenicity established. 

7. Of the Animal parasites the eel worm (Heterodera radicicola) 
has been shown to produce a root gall disease of the sweet pea. The 
disease is carefully described. The eel worm has also been shown to 
open the way to the attacks of several fungous diseases. 

8. Sclerotinia libertiana has been shown for the first time to pro- 
duce a collar rot as well as a stem disease of the sweet pea. 

9. Studies on the mildew of the sweet pea have shown the disease 
to be very prevalent under greenhouse conditions as well as out of 
doors. The cause of the mildew is a species of Oidium. Observations 
up to date have failed to reveal the perfect stage of the fungus. 



86 

10. Extended studies and cross inoculations have definitely proven 
that the anthracnose disease of the sweet pea and the bitter rot of 'the 
apple are caused by the same fungus Glomerella rufomaculans. 

11. It has been also proven that the following pathogens, namely, 
Gloeosporium gallarum from oak gall, Gloes. diospyri from persim- 
mon fruit, Gloe. officinale from the Sassafras, Colletotrichum nigrum 
from the pepper plant, Colletotrichum phomoides from the tomato, 
appear to be identical and the same as Glomerella rufomaculans, since 
they can all produce the anthracnose disease of the sweet pea and the 
bitter rot of the apple. Cross inoculations would no doubt reduce the 
great number of our so-called different species of Gloeosporiums. 

12. The mosaic has been shown for the first time to produce a dis- 
ease on the sweet pea. The pathogenicity and the infectious nature 
of the disease have been clearly demonstrated. Exceptions are taken 
with Woods that the disease is of a physiological nature but that it is 
induced by either bacteria or protozoa which neither our microscope 
nor our present method of staining are able to detect. Insects and 
especially the green aphids seem to be the main carriers and distrib- 
utors of the disease. 

13. Manns and Taubenhaus have definitely proven that the 
"streak" disease is caused by Bacillus lathyri M. & T. and not by 
Thielavia basicola as previously believed by Massee and Chittenden. 

14. Bud Drop in one form is here shown to be induced by a high 
nitrogen supply not properly balanced by phosphoric acid and pot- 
ash; by addition of the latter the trouble is quickly corrected. Ar- 
rested development may be due to overtreatment of soil with wood 
ashes the treatment being too caustic. Such an error may be corrected 
by the addition of acid phosphate. 

15. Under methods of control it is shown that no one variety is 
immune to the anthracnose but there are certain individuals in each 
variety which are more or less immune to the disease. 

16. Boiling the seeds for one or two seconds destroys the spores of 
parasitic fungi, but commercially the treatment is not applicable on 
large quantities of seed at a time. 

17. Soaking the seeds in sulphuric acid for five minutes, fifteen 
minutes and one-half hour increases 'the per cent of germination and 
at the same time kills all the spores which adhere to the seed coat. 



87 

18. Soaking the seeds in a 5% formaldehyde solution from five 
minutes to one hour does not iinerease nor decrease the percent of ger- 
mination but helps to kill the spores which adhere to the seed coat. 

19. Watering soils with chemical poisons does not increase the 
resistance of the plants which are grown on that soil. The latter 
adsorbs and fixes some of these poisons so as to make them harmless 
to plant growth. 

20. A new method has been devised in determining the length of 
time in which any fungicide can remain efficient in controlling plant 
diseases when sprayed on the plant to be treated. 



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89 

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